- How do I install packages in R?
- How do I load packages in R?
- How do a read a CSV file in R?
- How does R store tabular data?
- How does R decide what data types to use for columns in CSV data?
- How can I inspect tabular data that I have loaded or created?
- How can I select sections of tabular data?
- How can I extract vectors from tables?
- How can I calculate basic statistics on tabular data?
- How does R treat missing data when calculating aggregate statistics?
- How can I control how R treats missing data when calculating aggregate statistics?
- What tools does the tidyverse provide for selecting, rearranging, changing, and summarizing tabular data?
- How should I combine tidyverse operations?

Subsetting data frames:When we are working with data frames (including tibbles), subsetting with a single vector selects columns, not rows, because data frames are stored as lists of columns. This means that`df[1:2]`

selects two columns from`df`

. However, in`df[2:3, 1:2]`

, the first index selects rows, while the second selects columns.

There is no point in becoming fluent in Enochian if you do not then summon a Dweller Beneath at the time of the new moon. Similarly, there is no point learning a language designed for data manipulation if you do not then bend data to your will.

We begin by looking at the file `tidy/infant_hiv.csv`

,
a tidied version of data on the percentage of infants born to women with HIV
who received an HIV test themselves within two months of birth.
The original data comes from the UNICEF site at https://data.unicef.org/resources/dataset/hiv-aids-statistical-tables/,
and this file contains:

```
country,year,estimate,hi,lo
AFG,2009,NA,NA,NA
AFG,2010,NA,NA,NA
...
AFG,2017,NA,NA,NA
AGO,2009,NA,NA,NA
AGO,2010,0.03,0.04,0.02
AGO,2011,0.05,0.07,0.04
AGO,2012,0.06,0.08,0.05
...
ZWE,2016,0.71,0.88,0.62
ZWE,2017,0.65,0.81,0.57
```

The actual file has many more rows and no ellipses.
It uses `NA`

to show missing data rather than (for example) `-`

, a space, or a blank,
and its values are interpreted as follows:

Header | Datatype | Description |
---|---|---|

country | char | ISO3 country code of country reporting data |

year | integer | year CE for which data reported |

estimate | double/NA | estimated percentage of measurement |

hi | double/NA | high end of range |

lo | double/NA | low end of range |

```
import pandas as pd
data = pd.read_csv('tidy/infant_hiv.csv')
print(data)
#> country year estimate hi lo
#> 0 AFG 2009 NaN NaN NaN
#> 1 AFG 2010 NaN NaN NaN
#> 2 AFG 2011 NaN NaN NaN
#> 3 AFG 2012 NaN NaN NaN
#> 4 AFG 2013 NaN NaN NaN
#> 5 AFG 2014 NaN NaN NaN
#> 6 AFG 2015 NaN NaN NaN
#> 7 AFG 2016 NaN NaN NaN
#> 8 AFG 2017 NaN NaN NaN
#> 9 AGO 2009 NaN NaN NaN
#> 10 AGO 2010 0.03 0.04 0.02
#> 11 AGO 2011 0.05 0.07 0.04
#> 12 AGO 2012 0.06 0.08 0.05
#> 13 AGO 2013 0.15 0.20 0.12
#> 14 AGO 2014 0.10 0.14 0.08
#> 15 AGO 2015 0.06 0.08 0.05
#> 16 AGO 2016 0.01 0.02 0.01
#> 17 AGO 2017 0.01 0.02 0.01
#> 18 AIA 2009 NaN NaN NaN
#> 19 AIA 2010 NaN NaN NaN
#> 20 AIA 2011 NaN NaN NaN
#> 21 AIA 2012 NaN NaN NaN
#> 22 AIA 2013 NaN NaN NaN
#> 23 AIA 2014 NaN NaN NaN
#> 24 AIA 2015 NaN NaN NaN
#> 25 AIA 2016 NaN NaN NaN
#> 26 AIA 2017 NaN NaN NaN
#> 27 ALB 2009 NaN NaN NaN
#> 28 ALB 2010 NaN NaN NaN
#> 29 ALB 2011 NaN NaN NaN
#> ... ... ... ... ... ...
#> 1698 YEM 2015 NaN NaN NaN
#> 1699 YEM 2016 NaN NaN NaN
#> 1700 YEM 2017 NaN NaN NaN
#> 1701 ZAF 2009 NaN NaN NaN
#> 1702 ZAF 2010 0.66 0.88 0.56
#> 1703 ZAF 2011 0.65 0.86 0.54
#> 1704 ZAF 2012 0.89 0.95 0.75
#> 1705 ZAF 2013 0.75 0.95 0.63
#> 1706 ZAF 2014 0.86 0.95 0.73
#> 1707 ZAF 2015 0.95 0.95 0.95
#> 1708 ZAF 2016 0.79 0.95 0.67
#> 1709 ZAF 2017 0.95 0.95 0.85
#> 1710 ZMB 2009 0.59 0.70 0.53
#> 1711 ZMB 2010 0.27 0.32 0.24
#> 1712 ZMB 2011 0.70 0.84 0.63
#> 1713 ZMB 2012 0.74 0.88 0.67
#> 1714 ZMB 2013 0.64 0.76 0.57
#> 1715 ZMB 2014 0.91 0.95 0.81
#> 1716 ZMB 2015 0.43 0.52 0.39
#> 1717 ZMB 2016 0.43 0.51 0.39
#> 1718 ZMB 2017 0.46 0.54 0.41
#> 1719 ZWE 2009 NaN NaN NaN
#> 1720 ZWE 2010 0.12 0.15 0.10
#> 1721 ZWE 2011 0.23 0.28 0.20
#> 1722 ZWE 2012 0.38 0.47 0.33
#> 1723 ZWE 2013 0.57 0.70 0.49
#> 1724 ZWE 2014 0.54 0.67 0.47
#> 1725 ZWE 2015 0.59 0.73 0.51
#> 1726 ZWE 2016 0.71 0.88 0.62
#> 1727 ZWE 2017 0.65 0.81 0.57
#>
#> [1728 rows x 5 columns]
```

The equivalent in R is to load the tidyverse collection of libraries
and then call the `read_csv`

function.
We will go through this in stages, since each produces output.

```
library(tidyverse)
```

```
Error in library(tidyverse) : there is no package called 'tidyverse'
```

Ah.
We must install this (which we only need to do once per machine) and then load it.
Note that to install, we give `install.packages`

a string,
but to use,
we simply give the name of the library we want:

```
install.packages("tidyverse")
#> Error in contrib.url(repos, "source"): trying to use CRAN without setting a mirror
library(tidyverse)
```

Asking for the tidyverse gives us eight libraries (or packages](../glossary/#package)).
One of those, dplyr, defines two functions that mask standard functions in R with the same names.
This is deliberate, and if we need the originals, we can get them with their fully-qualified names
`stats::filter`

and `stats::lag`

.
(Note that R uses `::`

to get functions out of packages rather than Python’s `.`

.)

Once we have the tidyverse loaded, reading the file looks remarkably like reading the file:

```
data <- read_csv('tidy/infant_hiv.csv')
#> Parsed with column specification:
#> cols(
#> country = col_character(),
#> year = col_integer(),
#> estimate = col_double(),
#> hi = col_double(),
#> lo = col_double()
#> )
```

R’s `read_csv`

tells us more about what it has done than Pandas does.
In particular, it guesses at columns’ data types based on the first thousand values,
and then tells us what types it has inferred.
(In a better universe,
people habitually use the first *two* rows of their spreadsheets for name *and units*,
but we do not live there.)

We can now look at what `read_csv`

has produced.

```
data
#> # A tibble: 1,728 x 5
#> country year estimate hi lo
#> <chr> <int> <dbl> <dbl> <dbl>
#> 1 AFG 2009 NA NA NA
#> 2 AFG 2010 NA NA NA
#> 3 AFG 2011 NA NA NA
#> 4 AFG 2012 NA NA NA
#> 5 AFG 2013 NA NA NA
#> 6 AFG 2014 NA NA NA
#> 7 AFG 2015 NA NA NA
#> 8 AFG 2016 NA NA NA
#> 9 AFG 2017 NA NA NA
#> 10 AGO 2009 NA NA NA
#> # … with 1,718 more rows
```

This is a tibble,
which is the tidyverse’s enhanced version of R’s `data.frame`

.
It organizes data into named columns,
each having one value for each row.

We often have a quick look at the content of a table to remind ourselves what it contains.
Pandas does this using methods whose names are borrowed from the Unix shell’s `head`

and `tail`

commands:

```
print(data.head())
#> country year estimate hi lo
#> 0 AFG 2009 NaN NaN NaN
#> 1 AFG 2010 NaN NaN NaN
#> 2 AFG 2011 NaN NaN NaN
#> 3 AFG 2012 NaN NaN NaN
#> 4 AFG 2013 NaN NaN NaN
```

```
print(data.tail())
#> country year estimate hi lo
#> 1723 ZWE 2013 0.57 0.70 0.49
#> 1724 ZWE 2014 0.54 0.67 0.47
#> 1725 ZWE 2015 0.59 0.73 0.51
#> 1726 ZWE 2016 0.71 0.88 0.62
#> 1727 ZWE 2017 0.65 0.81 0.57
```

R has similarly-named functions (not methods):

```
head(data)
#> # A tibble: 6 x 5
#> country year estimate hi lo
#> <chr> <int> <dbl> <dbl> <dbl>
#> 1 AFG 2009 NA NA NA
#> 2 AFG 2010 NA NA NA
#> 3 AFG 2011 NA NA NA
#> 4 AFG 2012 NA NA NA
#> 5 AFG 2013 NA NA NA
#> 6 AFG 2014 NA NA NA
```

```
tail(data)
#> # A tibble: 6 x 5
#> country year estimate hi lo
#> <chr> <int> <dbl> <dbl> <dbl>
#> 1 ZWE 2012 0.38 0.47 0.33
#> 2 ZWE 2013 0.570 0.7 0.49
#> 3 ZWE 2014 0.54 0.67 0.47
#> 4 ZWE 2015 0.59 0.73 0.51
#> 5 ZWE 2016 0.71 0.88 0.62
#> 6 ZWE 2017 0.65 0.81 0.570
```

Let’s have a closer look at that last command’s output:

```
tail(data)
#> # A tibble: 6 x 5
#> country year estimate hi lo
#> <chr> <int> <dbl> <dbl> <dbl>
#> 1 ZWE 2012 0.38 0.47 0.33
#> 2 ZWE 2013 0.570 0.7 0.49
#> 3 ZWE 2014 0.54 0.67 0.47
#> 4 ZWE 2015 0.59 0.73 0.51
#> 5 ZWE 2016 0.71 0.88 0.62
#> 6 ZWE 2017 0.65 0.81 0.570
```

Note that the row numbers printed by `tail`

are relative to the output,
not absolute to the table.
This is different from Pandas,
which retains the original row numbers.
(Notice also that R starts numbering from 1.)
What about overall information?

```
print(data.info())
#> <class 'pandas.core.frame.DataFrame'>
#> RangeIndex: 1728 entries, 0 to 1727
#> Data columns (total 5 columns):
#> country 1728 non-null object
#> year 1728 non-null int64
#> estimate 728 non-null float64
#> hi 728 non-null float64
#> lo 728 non-null float64
#> dtypes: float64(3), int64(1), object(1)
#> memory usage: 67.6+ KB
#> None
```

```
summary(data)
#> country year estimate hi
#> Length:1728 Min. :2009 Min. :0.000 Min. :0.0000
#> Class :character 1st Qu.:2011 1st Qu.:0.100 1st Qu.:0.1400
#> Mode :character Median :2013 Median :0.340 Median :0.4350
#> Mean :2013 Mean :0.387 Mean :0.4614
#> 3rd Qu.:2015 3rd Qu.:0.620 3rd Qu.:0.7625
#> Max. :2017 Max. :0.950 Max. :0.9500
#> NA's :1000 NA's :1000
#> lo
#> Min. :0.0000
#> 1st Qu.:0.0800
#> Median :0.2600
#> Mean :0.3221
#> 3rd Qu.:0.5100
#> Max. :0.9500
#> NA's :1000
```

Your display of R’s summary may or may not wrap, depending on how large a screen the older acolytes have allowed you.

A Pandas DataFrame is a collection of series (also called columns), each containing the values of a single observed variable. Columns in R tibbles are, not coincidentally, the same.

```
print(data['estimate'])
#> 0 NaN
#> 1 NaN
#> 2 NaN
#> 3 NaN
#> 4 NaN
#> 5 NaN
#> 6 NaN
#> 7 NaN
#> 8 NaN
#> 9 NaN
#> 10 0.03
#> 11 0.05
#> 12 0.06
#> 13 0.15
#> 14 0.10
#> 15 0.06
#> 16 0.01
#> 17 0.01
#> 18 NaN
#> 19 NaN
#> 20 NaN
#> 21 NaN
#> 22 NaN
#> 23 NaN
#> 24 NaN
#> 25 NaN
#> 26 NaN
#> 27 NaN
#> 28 NaN
#> 29 NaN
#> ...
#> 1698 NaN
#> 1699 NaN
#> 1700 NaN
#> 1701 NaN
#> 1702 0.66
#> 1703 0.65
#> 1704 0.89
#> 1705 0.75
#> 1706 0.86
#> 1707 0.95
#> 1708 0.79
#> 1709 0.95
#> 1710 0.59
#> 1711 0.27
#> 1712 0.70
#> 1713 0.74
#> 1714 0.64
#> 1715 0.91
#> 1716 0.43
#> 1717 0.43
#> 1718 0.46
#> 1719 NaN
#> 1720 0.12
#> 1721 0.23
#> 1722 0.38
#> 1723 0.57
#> 1724 0.54
#> 1725 0.59
#> 1726 0.71
#> 1727 0.65
#> Name: estimate, Length: 1728, dtype: float64
```

We would get exactly the same output in Python with `data.estimate`

,
i.e.,
with an attribute name rather than a string subscript.
The same tricks work in R:

```
data['estimate']
#> # A tibble: 1,728 x 1
#> estimate
#> <dbl>
#> 1 NA
#> 2 NA
#> 3 NA
#> 4 NA
#> 5 NA
#> 6 NA
#> 7 NA
#> 8 NA
#> 9 NA
#> 10 NA
#> # … with 1,718 more rows
```

However, R’s `data$estimate`

provides all the data:

```
data$estimate
#> [1] NA NA NA NA NA NA NA NA NA NA 0.03 0.05 0.06
#> [14] 0.15 0.10 0.06 0.01 0.01 NA NA NA NA NA NA NA NA
#> [27] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [40] NA NA NA NA NA NA NA NA 0.13 0.12 0.12 0.52 0.53
#> [53] 0.67 0.66 NA NA NA NA NA NA NA NA NA NA NA
#> [66] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [79] NA NA NA NA NA NA NA NA NA NA NA NA 0.26
#> [92] 0.24 0.38 0.55 0.61 0.74 0.83 0.75 0.74 NA 0.10 0.10 0.11 0.18
#> [105] 0.12 0.02 0.12 0.20 NA NA NA NA NA NA NA NA NA
#> [118] NA NA 0.10 0.09 0.12 0.26 0.27 0.25 0.32 0.03 0.09 0.13 0.19
#> [131] 0.25 0.30 0.28 0.15 0.16 NA 0.02 0.02 0.02 0.03 0.15 0.10 0.17
#> [144] 0.14 NA NA NA NA NA NA NA NA NA NA NA NA
#> [157] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [170] NA NA NA NA NA NA NA NA NA NA NA 0.95 0.95
#> [183] 0.95 0.95 0.95 0.95 0.80 0.95 0.87 0.77 0.75 0.72 0.51 0.55 0.50
#> [196] 0.62 0.37 0.36 0.07 0.46 0.46 0.46 0.46 0.44 0.43 0.42 0.40 0.25
#> [209] 0.25 0.46 0.25 0.45 0.45 0.46 0.46 0.45 NA NA NA NA NA
#> [222] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [235] NA NA NA NA NA NA NA NA NA NA 0.53 0.35 0.36
#> [248] 0.48 0.41 0.45 0.47 0.50 0.01 0.01 0.07 0.05 0.03 0.09 0.12 0.21
#> [261] 0.23 NA NA NA NA NA NA NA NA NA NA NA NA
#> [274] NA NA NA NA NA NA NA NA 0.64 0.56 0.67 0.77 0.92
#> [287] 0.70 0.85 NA NA NA NA NA NA NA NA NA NA 0.22
#> [300] 0.03 0.19 0.12 0.33 0.28 0.39 0.40 0.27 0.20 0.25 0.30 0.32 0.36
#> [313] 0.33 0.53 0.51 NA 0.03 0.05 0.07 0.10 0.14 0.16 0.20 0.34 0.08
#> [326] 0.07 0.03 0.05 0.04 0.00 0.01 0.02 0.03 NA NA NA NA NA
#> [339] NA NA NA NA 0.05 0.10 0.18 0.22 0.30 0.37 0.45 0.44 0.48
#> [352] NA NA NA NA NA NA NA NA NA 0.95 0.95 0.95 0.76
#> [365] 0.85 0.94 0.70 0.94 0.93 0.92 0.69 0.66 0.89 0.66 0.78 0.79 0.64
#> [378] 0.71 0.83 0.95 0.95 0.95 0.95 0.92 0.95 0.95 0.95 NA NA NA
#> [391] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [404] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [417] 0.02 0.08 0.08 0.02 0.08 0.10 0.10 NA NA NA NA NA NA
#> [430] NA NA NA NA NA NA NA NA NA NA NA NA 0.28
#> [443] 0.10 0.43 0.46 0.64 0.95 0.95 0.72 0.80 NA NA 0.38 0.23 0.55
#> [456] 0.27 0.23 0.33 0.61 0.01 0.01 0.95 0.87 0.21 0.87 0.54 0.70 0.69
#> [469] 0.04 0.05 0.04 0.04 0.04 0.05 0.07 0.10 0.11 NA NA NA NA
#> [482] 0.27 0.39 0.36 0.39 0.15 NA NA NA NA NA NA NA NA
#> [495] NA NA NA NA NA NA NA NA NA NA 0.04 0.40 0.15
#> [508] 0.24 0.24 0.25 0.31 0.45 0.38 NA NA NA NA NA NA NA
#> [521] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [534] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [547] NA NA NA NA 0.06 0.27 0.28 0.16 0.20 0.24 0.24 0.04 NA
#> [560] NA NA NA NA NA NA NA NA 0.61 0.82 0.69 0.62 0.58
#> [573] 0.74 0.77 0.79 0.84 NA 0.01 0.11 0.09 0.19 0.15 0.20 0.31 0.30
#> [586] NA 0.05 0.06 0.00 0.06 0.07 0.04 0.39 0.11 NA NA NA NA
#> [599] NA 0.08 0.11 0.12 0.12 NA NA 0.00 0.03 0.05 0.24 0.35 0.36
#> [612] 0.36 NA NA NA NA NA NA NA NA NA NA NA NA
#> [625] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [638] NA NA NA NA 0.19 0.17 0.11 0.15 0.15 0.15 0.17 NA 0.27
#> [651] 0.47 0.38 0.32 0.60 0.55 0.54 0.53 0.61 0.69 0.89 0.43 0.47 0.49
#> [664] 0.40 0.60 0.59 NA NA NA NA NA NA NA NA NA NA
#> [677] NA 0.04 0.39 0.35 0.36 0.32 0.35 0.40 NA NA NA NA NA
#> [690] NA NA NA NA NA NA NA NA 0.04 0.05 0.06 0.02 0.01
#> [703] NA 0.06 0.07 0.08 0.09 0.10 0.25 0.27 0.23 NA NA NA NA
#> [716] NA NA NA NA NA 0.02 0.13 0.03 0.09 0.12 0.15 0.20 0.23
#> [729] 0.31 NA NA NA NA NA NA NA NA NA NA NA NA
#> [742] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [755] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [768] 0.63 NA 0.68 0.59 NA NA NA NA NA NA NA NA NA
#> [781] NA NA NA NA NA NA NA NA NA NA NA NA 0.95
#> [794] 0.95 0.95 0.95 0.95 0.95 0.84 0.76 0.82 NA 0.75 0.46 0.45 0.45
#> [807] 0.74 0.51 0.56 0.51 NA NA 0.03 0.11 0.11 0.38 0.33 0.66 0.70
#> [820] NA 0.45 0.62 0.34 0.37 0.37 0.79 0.74 0.64 NA NA NA NA
#> [833] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [846] NA NA NA NA NA NA NA NA NA NA NA 0.01 0.08
#> [859] 0.06 0.10 0.03 0.03 0.07 0.07 NA NA NA NA NA NA NA
#> [872] NA NA 0.05 0.05 0.17 0.28 0.31 0.13 NA NA NA NA NA
#> [885] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [898] NA NA NA NA NA NA NA NA NA NA NA NA 0.43
#> [911] 0.95 0.95 0.70 0.47 0.51 0.87 0.58 0.51 NA NA NA NA NA
#> [924] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [937] NA NA NA NA NA NA NA NA NA 0.02 0.21 0.21 0.68
#> [950] 0.65 0.62 0.61 0.59 0.57 0.95 0.95 0.95 0.95 0.95 0.95 0.95 0.95
#> [963] 0.95 NA NA 0.00 0.01 NA NA NA NA NA NA NA NA
#> [976] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [989] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [1002] NA NA NA NA NA NA NA 0.08 0.08 0.08 0.10 0.08 0.06
#> [1015] 0.03 0.11 0.11 NA NA NA NA NA NA NA NA NA NA
#> [1028] 0.01 0.04 0.05 0.09 0.12 0.15 0.26 0.28 NA NA NA NA NA
#> [1041] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [1054] NA 0.31 0.36 0.30 0.31 0.38 0.41 0.44 0.50 NA NA NA NA
#> [1067] NA NA NA 0.08 0.08 NA NA NA NA NA NA NA NA
#> [1080] NA NA NA NA 0.06 0.17 0.21 0.20 0.31 0.52 0.37 0.61 0.68
#> [1093] 0.68 0.77 0.87 0.75 0.69 0.95 NA 0.57 0.85 0.59 0.55 0.91 0.17
#> [1106] 0.53 0.95 NA NA NA 0.01 0.09 0.02 0.11 0.05 0.10 0.04 0.06
#> [1119] 0.07 0.06 0.05 0.06 0.10 0.11 0.12 0.50 0.38 0.95 0.47 0.57 0.51
#> [1132] 0.65 0.60 0.75 NA NA NA NA NA NA NA NA NA NA
#> [1145] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [1158] NA NA NA NA 0.02 0.03 0.05 0.09 0.05 0.08 0.21 0.26 0.45
#> [1171] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [1184] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [1197] NA 0.01 0.01 0.01 0.00 0.01 0.01 0.00 0.00 0.01 NA 0.30 0.39
#> [1210] 0.20 0.39 0.45 0.55 0.51 0.49 NA NA 0.13 0.25 0.36 0.29 0.63
#> [1223] 0.41 0.78 0.01 0.03 0.05 0.03 0.00 0.02 0.03 0.04 0.05 NA NA
#> [1236] NA NA NA NA NA NA NA NA NA 0.23 0.18 0.53 0.30
#> [1249] 0.37 0.36 0.35 NA NA NA NA NA NA NA NA NA NA
#> [1262] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [1275] NA NA NA NA NA 0.27 0.34 0.50 0.39 0.38 0.47 0.52 0.52
#> [1288] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [1301] NA NA NA NA NA NA NA NA NA NA 0.64 0.58 0.54
#> [1314] 0.84 0.58 0.73 0.74 0.81 0.83 0.87 0.84 0.90 0.85 NA NA NA
#> [1327] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [1340] NA NA 0.11 0.11 0.09 0.10 0.12 0.12 0.16 0.13 0.23 NA NA
#> [1353] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [1366] NA NA NA NA 0.01 0.01 0.02 0.25 0.02 0.03 0.06 0.07 NA
#> [1379] 0.28 0.28 0.02 0.31 0.40 0.40 0.35 0.34 NA NA NA NA NA
#> [1392] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [1405] NA NA NA NA NA NA 0.01 0.03 0.10 NA NA NA NA
#> [1418] NA NA NA NA NA 0.09 0.09 0.09 0.34 0.58 0.81 0.95 0.95
#> [1431] 0.67 NA NA NA NA NA NA NA NA NA NA NA NA
#> [1444] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [1457] NA NA NA 0.50 0.93 0.95 0.87 0.84 0.88 0.82 0.81 NA NA
#> [1470] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [1483] NA NA NA NA 0.03 0.02 0.06 0.06 0.07 0.05 0.05 0.05 0.07
#> [1496] 0.14 0.05 0.11 0.11 0.16 0.17 0.36 0.36 NA 0.54 0.56 0.64 0.68
#> [1509] 0.70 0.92 0.92 0.94 0.01 0.04 0.08 0.11 0.14 0.14 0.30 0.21 0.43
#> [1522] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [1535] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [1548] NA NA NA NA 0.37 0.50 0.95 0.83 0.90 0.94 NA NA 0.16
#> [1561] 0.14 0.18 0.33 0.40 0.31 0.13 NA NA NA NA NA NA NA
#> [1574] NA NA NA NA NA NA NA NA NA NA NA 0.13 0.24
#> [1587] 0.30 0.29 0.29 0.39 0.38 0.39 0.36 0.08 0.13 0.38 0.45 0.50 0.69
#> [1600] 0.43 0.35 0.48 0.78 0.95 0.81 0.88 0.95 0.78 0.47 0.55 0.48 NA
#> [1613] NA NA NA NA NA NA NA NA NA 0.62 0.68 0.85 0.95
#> [1626] 0.95 0.95 0.90 0.95 NA NA NA NA NA NA NA NA NA
#> [1639] 0.00 0.12 0.58 0.54 0.48 0.84 0.76 0.74 0.56 NA NA NA NA
#> [1652] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [1665] NA NA NA 0.31 0.30 0.63 0.41 0.49 0.49 0.31 NA NA NA
#> [1678] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [1691] NA NA NA NA NA NA NA NA NA NA NA NA 0.66
#> [1704] 0.65 0.89 0.75 0.86 0.95 0.79 0.95 0.59 0.27 0.70 0.74 0.64 0.91
#> [1717] 0.43 0.43 0.46 NA 0.12 0.23 0.38 0.57 0.54 0.59 0.71 0.65
```

Again, note that the boxed number on the left is the start index of that row.

What about single values? Remembering to count from zero from Python and as humans do for R, we have:

```
print(data.estimate[11])
#> 0.05
```

```
data$estimate[12]
#> [1] 0.05
```

Ah—everything in R is a vector, so we get a vector of one value as an output rather than a single value.

```
print(len(data.estimate[11]))
#> TypeError: object of type 'numpy.float64' has no len()
#>
#> Detailed traceback:
#> File "<string>", line 1, in <module>
```

```
length(data$estimate[12])
#> [1] 1
```

And yes, ranges work:

```
print(data.estimate[5:15])
#> 5 NaN
#> 6 NaN
#> 7 NaN
#> 8 NaN
#> 9 NaN
#> 10 0.03
#> 11 0.05
#> 12 0.06
#> 13 0.15
#> 14 0.10
#> Name: estimate, dtype: float64
```

```
data$estimate[6:15]
#> [1] NA NA NA NA NA 0.03 0.05 0.06 0.15 0.10
```

Note that the upper bound is the same, because it’s inclusive in R and exclusive in Python. Note also that neither library prevents us from selecting a range of data that spans logical groups such as countries, which is why selecting by row number is usually a sign of innocence, insouciance, or desperation.

We can select by column number as well.
Pandas uses the rather clumsy `object.iloc[rows, columns]`

, with the usual `:`

shortcut for “entire range”:

```
print(data.iloc[:, 0])
#> 0 AFG
#> 1 AFG
#> 2 AFG
#> 3 AFG
#> 4 AFG
#> 5 AFG
#> 6 AFG
#> 7 AFG
#> 8 AFG
#> 9 AGO
#> 10 AGO
#> 11 AGO
#> 12 AGO
#> 13 AGO
#> 14 AGO
#> 15 AGO
#> 16 AGO
#> 17 AGO
#> 18 AIA
#> 19 AIA
#> 20 AIA
#> 21 AIA
#> 22 AIA
#> 23 AIA
#> 24 AIA
#> 25 AIA
#> 26 AIA
#> 27 ALB
#> 28 ALB
#> 29 ALB
#> ...
#> 1698 YEM
#> 1699 YEM
#> 1700 YEM
#> 1701 ZAF
#> 1702 ZAF
#> 1703 ZAF
#> 1704 ZAF
#> 1705 ZAF
#> 1706 ZAF
#> 1707 ZAF
#> 1708 ZAF
#> 1709 ZAF
#> 1710 ZMB
#> 1711 ZMB
#> 1712 ZMB
#> 1713 ZMB
#> 1714 ZMB
#> 1715 ZMB
#> 1716 ZMB
#> 1717 ZMB
#> 1718 ZMB
#> 1719 ZWE
#> 1720 ZWE
#> 1721 ZWE
#> 1722 ZWE
#> 1723 ZWE
#> 1724 ZWE
#> 1725 ZWE
#> 1726 ZWE
#> 1727 ZWE
#> Name: country, Length: 1728, dtype: object
```

Since this is a column, it can be indexed:

```
print(data.iloc[:, 0][0])
#> AFG
```

In R, a single index is interpreted as the column index:

```
data[1]
#> # A tibble: 1,728 x 1
#> country
#> <chr>
#> 1 AFG
#> 2 AFG
#> 3 AFG
#> 4 AFG
#> 5 AFG
#> 6 AFG
#> 7 AFG
#> 8 AFG
#> 9 AFG
#> 10 AGO
#> # … with 1,718 more rows
```

But notice that the output is not a vector, but another tibble (i.e., an N-row, 1-column structure). This means that adding another index does column-wise indexing on that tibble:

```
data[1][1]
#> # A tibble: 1,728 x 1
#> country
#> <chr>
#> 1 AFG
#> 2 AFG
#> 3 AFG
#> 4 AFG
#> 5 AFG
#> 6 AFG
#> 7 AFG
#> 8 AFG
#> 9 AFG
#> 10 AGO
#> # … with 1,718 more rows
```

How then are we to get the first mention of Afghanistan? The answer is to use double square brackets to strip away one level of structure:

```
data[[1]]
#> [1] "AFG" "AFG" "AFG" "AFG" "AFG" "AFG" "AFG" "AFG" "AFG" "AGO" "AGO"
#> [12] "AGO" "AGO" "AGO" "AGO" "AGO" "AGO" "AGO" "AIA" "AIA" "AIA" "AIA"
#> [23] "AIA" "AIA" "AIA" "AIA" "AIA" "ALB" "ALB" "ALB" "ALB" "ALB" "ALB"
#> [34] "ALB" "ALB" "ALB" "ARE" "ARE" "ARE" "ARE" "ARE" "ARE" "ARE" "ARE"
#> [45] "ARE" "ARG" "ARG" "ARG" "ARG" "ARG" "ARG" "ARG" "ARG" "ARG" "ARM"
#> [56] "ARM" "ARM" "ARM" "ARM" "ARM" "ARM" "ARM" "ARM" "ATG" "ATG" "ATG"
#> [67] "ATG" "ATG" "ATG" "ATG" "ATG" "ATG" "AUS" "AUS" "AUS" "AUS" "AUS"
#> [78] "AUS" "AUS" "AUS" "AUS" "AUT" "AUT" "AUT" "AUT" "AUT" "AUT" "AUT"
#> [89] "AUT" "AUT" "AZE" "AZE" "AZE" "AZE" "AZE" "AZE" "AZE" "AZE" "AZE"
#> [100] "BDI" "BDI" "BDI" "BDI" "BDI" "BDI" "BDI" "BDI" "BDI" "BEL" "BEL"
#> [111] "BEL" "BEL" "BEL" "BEL" "BEL" "BEL" "BEL" "BEN" "BEN" "BEN" "BEN"
#> [122] "BEN" "BEN" "BEN" "BEN" "BEN" "BFA" "BFA" "BFA" "BFA" "BFA" "BFA"
#> [133] "BFA" "BFA" "BFA" "BGD" "BGD" "BGD" "BGD" "BGD" "BGD" "BGD" "BGD"
#> [144] "BGD" "BGR" "BGR" "BGR" "BGR" "BGR" "BGR" "BGR" "BGR" "BGR" "BHR"
#> [155] "BHR" "BHR" "BHR" "BHR" "BHR" "BHR" "BHR" "BHR" "BHS" "BHS" "BHS"
#> [166] "BHS" "BHS" "BHS" "BHS" "BHS" "BHS" "BIH" "BIH" "BIH" "BIH" "BIH"
#> [177] "BIH" "BIH" "BIH" "BIH" "BLR" "BLR" "BLR" "BLR" "BLR" "BLR" "BLR"
#> [188] "BLR" "BLR" "BLZ" "BLZ" "BLZ" "BLZ" "BLZ" "BLZ" "BLZ" "BLZ" "BLZ"
#> [199] "BOL" "BOL" "BOL" "BOL" "BOL" "BOL" "BOL" "BOL" "BOL" "BRA" "BRA"
#> [210] "BRA" "BRA" "BRA" "BRA" "BRA" "BRA" "BRA" "BRB" "BRB" "BRB" "BRB"
#> [221] "BRB" "BRB" "BRB" "BRB" "BRB" "BRN" "BRN" "BRN" "BRN" "BRN" "BRN"
#> [232] "BRN" "BRN" "BRN" "BTN" "BTN" "BTN" "BTN" "BTN" "BTN" "BTN" "BTN"
#> [243] "BTN" "BWA" "BWA" "BWA" "BWA" "BWA" "BWA" "BWA" "BWA" "BWA" "CAF"
#> [254] "CAF" "CAF" "CAF" "CAF" "CAF" "CAF" "CAF" "CAF" "CAN" "CAN" "CAN"
#> [265] "CAN" "CAN" "CAN" "CAN" "CAN" "CAN" "CHE" "CHE" "CHE" "CHE" "CHE"
#> [276] "CHE" "CHE" "CHE" "CHE" "CHL" "CHL" "CHL" "CHL" "CHL" "CHL" "CHL"
#> [287] "CHL" "CHL" "CHN" "CHN" "CHN" "CHN" "CHN" "CHN" "CHN" "CHN" "CHN"
#> [298] "CIV" "CIV" "CIV" "CIV" "CIV" "CIV" "CIV" "CIV" "CIV" "CMR" "CMR"
#> [309] "CMR" "CMR" "CMR" "CMR" "CMR" "CMR" "CMR" "COD" "COD" "COD" "COD"
#> [320] "COD" "COD" "COD" "COD" "COD" "COG" "COG" "COG" "COG" "COG" "COG"
#> [331] "COG" "COG" "COG" "COK" "COK" "COK" "COK" "COK" "COK" "COK" "COK"
#> [342] "COK" "COL" "COL" "COL" "COL" "COL" "COL" "COL" "COL" "COL" "COM"
#> [353] "COM" "COM" "COM" "COM" "COM" "COM" "COM" "COM" "CPV" "CPV" "CPV"
#> [364] "CPV" "CPV" "CPV" "CPV" "CPV" "CPV" "CRI" "CRI" "CRI" "CRI" "CRI"
#> [375] "CRI" "CRI" "CRI" "CRI" "CUB" "CUB" "CUB" "CUB" "CUB" "CUB" "CUB"
#> [386] "CUB" "CUB" "CYP" "CYP" "CYP" "CYP" "CYP" "CYP" "CYP" "CYP" "CYP"
#> [397] "CZE" "CZE" "CZE" "CZE" "CZE" "CZE" "CZE" "CZE" "CZE" "DEU" "DEU"
#> [408] "DEU" "DEU" "DEU" "DEU" "DEU" "DEU" "DEU" "DJI" "DJI" "DJI" "DJI"
#> [419] "DJI" "DJI" "DJI" "DJI" "DJI" "DMA" "DMA" "DMA" "DMA" "DMA" "DMA"
#> [430] "DMA" "DMA" "DMA" "DNK" "DNK" "DNK" "DNK" "DNK" "DNK" "DNK" "DNK"
#> [441] "DNK" "DOM" "DOM" "DOM" "DOM" "DOM" "DOM" "DOM" "DOM" "DOM" "DZA"
#> [452] "DZA" "DZA" "DZA" "DZA" "DZA" "DZA" "DZA" "DZA" "ECU" "ECU" "ECU"
#> [463] "ECU" "ECU" "ECU" "ECU" "ECU" "ECU" "EGY" "EGY" "EGY" "EGY" "EGY"
#> [474] "EGY" "EGY" "EGY" "EGY" "ERI" "ERI" "ERI" "ERI" "ERI" "ERI" "ERI"
#> [485] "ERI" "ERI" "ESP" "ESP" "ESP" "ESP" "ESP" "ESP" "ESP" "ESP" "ESP"
#> [496] "EST" "EST" "EST" "EST" "EST" "EST" "EST" "EST" "EST" "ETH" "ETH"
#> [507] "ETH" "ETH" "ETH" "ETH" "ETH" "ETH" "ETH" "FIN" "FIN" "FIN" "FIN"
#> [518] "FIN" "FIN" "FIN" "FIN" "FIN" "FJI" "FJI" "FJI" "FJI" "FJI" "FJI"
#> [529] "FJI" "FJI" "FJI" "FRA" "FRA" "FRA" "FRA" "FRA" "FRA" "FRA" "FRA"
#> [540] "FRA" "FSM" "FSM" "FSM" "FSM" "FSM" "FSM" "FSM" "FSM" "FSM" "GAB"
#> [551] "GAB" "GAB" "GAB" "GAB" "GAB" "GAB" "GAB" "GAB" "GBR" "GBR" "GBR"
#> [562] "GBR" "GBR" "GBR" "GBR" "GBR" "GBR" "GEO" "GEO" "GEO" "GEO" "GEO"
#> [573] "GEO" "GEO" "GEO" "GEO" "GHA" "GHA" "GHA" "GHA" "GHA" "GHA" "GHA"
#> [584] "GHA" "GHA" "GIN" "GIN" "GIN" "GIN" "GIN" "GIN" "GIN" "GIN" "GIN"
#> [595] "GMB" "GMB" "GMB" "GMB" "GMB" "GMB" "GMB" "GMB" "GMB" "GNB" "GNB"
#> [606] "GNB" "GNB" "GNB" "GNB" "GNB" "GNB" "GNB" "GNQ" "GNQ" "GNQ" "GNQ"
#> [617] "GNQ" "GNQ" "GNQ" "GNQ" "GNQ" "GRC" "GRC" "GRC" "GRC" "GRC" "GRC"
#> [628] "GRC" "GRC" "GRC" "GRD" "GRD" "GRD" "GRD" "GRD" "GRD" "GRD" "GRD"
#> [639] "GRD" "GTM" "GTM" "GTM" "GTM" "GTM" "GTM" "GTM" "GTM" "GTM" "GUY"
#> [650] "GUY" "GUY" "GUY" "GUY" "GUY" "GUY" "GUY" "GUY" "HND" "HND" "HND"
#> [661] "HND" "HND" "HND" "HND" "HND" "HND" "HRV" "HRV" "HRV" "HRV" "HRV"
#> [672] "HRV" "HRV" "HRV" "HRV" "HTI" "HTI" "HTI" "HTI" "HTI" "HTI" "HTI"
#> [683] "HTI" "HTI" "HUN" "HUN" "HUN" "HUN" "HUN" "HUN" "HUN" "HUN" "HUN"
#> [694] "IDN" "IDN" "IDN" "IDN" "IDN" "IDN" "IDN" "IDN" "IDN" "IND" "IND"
#> [705] "IND" "IND" "IND" "IND" "IND" "IND" "IND" "IRL" "IRL" "IRL" "IRL"
#> [716] "IRL" "IRL" "IRL" "IRL" "IRL" "IRN" "IRN" "IRN" "IRN" "IRN" "IRN"
#> [727] "IRN" "IRN" "IRN" "IRQ" "IRQ" "IRQ" "IRQ" "IRQ" "IRQ" "IRQ" "IRQ"
#> [738] "IRQ" "ISL" "ISL" "ISL" "ISL" "ISL" "ISL" "ISL" "ISL" "ISL" "ISR"
#> [749] "ISR" "ISR" "ISR" "ISR" "ISR" "ISR" "ISR" "ISR" "ITA" "ITA" "ITA"
#> [760] "ITA" "ITA" "ITA" "ITA" "ITA" "ITA" "JAM" "JAM" "JAM" "JAM" "JAM"
#> [771] "JAM" "JAM" "JAM" "JAM" "JOR" "JOR" "JOR" "JOR" "JOR" "JOR" "JOR"
#> [782] "JOR" "JOR" "JPN" "JPN" "JPN" "JPN" "JPN" "JPN" "JPN" "JPN" "JPN"
#> [793] "KAZ" "KAZ" "KAZ" "KAZ" "KAZ" "KAZ" "KAZ" "KAZ" "KAZ" "KEN" "KEN"
#> [804] "KEN" "KEN" "KEN" "KEN" "KEN" "KEN" "KEN" "KGZ" "KGZ" "KGZ" "KGZ"
#> [815] "KGZ" "KGZ" "KGZ" "KGZ" "KGZ" "KHM" "KHM" "KHM" "KHM" "KHM" "KHM"
#> [826] "KHM" "KHM" "KHM" "KIR" "KIR" "KIR" "KIR" "KIR" "KIR" "KIR" "KIR"
#> [837] "KIR" "KNA" "KNA" "KNA" "KNA" "KNA" "KNA" "KNA" "KNA" "KNA" "KOR"
#> [848] "KOR" "KOR" "KOR" "KOR" "KOR" "KOR" "KOR" "KOR" "LAO" "LAO" "LAO"
#> [859] "LAO" "LAO" "LAO" "LAO" "LAO" "LAO" "LBN" "LBN" "LBN" "LBN" "LBN"
#> [870] "LBN" "LBN" "LBN" "LBN" "LBR" "LBR" "LBR" "LBR" "LBR" "LBR" "LBR"
#> [881] "LBR" "LBR" "LBY" "LBY" "LBY" "LBY" "LBY" "LBY" "LBY" "LBY" "LBY"
#> [892] "LCA" "LCA" "LCA" "LCA" "LCA" "LCA" "LCA" "LCA" "LCA" "LKA" "LKA"
#> [903] "LKA" "LKA" "LKA" "LKA" "LKA" "LKA" "LKA" "LSO" "LSO" "LSO" "LSO"
#> [914] "LSO" "LSO" "LSO" "LSO" "LSO" "LTU" "LTU" "LTU" "LTU" "LTU" "LTU"
#> [925] "LTU" "LTU" "LTU" "LUX" "LUX" "LUX" "LUX" "LUX" "LUX" "LUX" "LUX"
#> [936] "LUX" "LVA" "LVA" "LVA" "LVA" "LVA" "LVA" "LVA" "LVA" "LVA" "MAR"
#> [947] "MAR" "MAR" "MAR" "MAR" "MAR" "MAR" "MAR" "MAR" "MDA" "MDA" "MDA"
#> [958] "MDA" "MDA" "MDA" "MDA" "MDA" "MDA" "MDG" "MDG" "MDG" "MDG" "MDG"
#> [969] "MDG" "MDG" "MDG" "MDG" "MDV" "MDV" "MDV" "MDV" "MDV" "MDV" "MDV"
#> [980] "MDV" "MDV" "MEX" "MEX" "MEX" "MEX" "MEX" "MEX" "MEX" "MEX" "MEX"
#> [991] "MHL" "MHL" "MHL" "MHL" "MHL" "MHL" "MHL" "MHL" "MHL" "MKD" "MKD"
#> [1002] "MKD" "MKD" "MKD" "MKD" "MKD" "MKD" "MKD" "MLI" "MLI" "MLI" "MLI"
#> [1013] "MLI" "MLI" "MLI" "MLI" "MLI" "MLT" "MLT" "MLT" "MLT" "MLT" "MLT"
#> [1024] "MLT" "MLT" "MLT" "MMR" "MMR" "MMR" "MMR" "MMR" "MMR" "MMR" "MMR"
#> [1035] "MMR" "MNE" "MNE" "MNE" "MNE" "MNE" "MNE" "MNE" "MNE" "MNE" "MNG"
#> [1046] "MNG" "MNG" "MNG" "MNG" "MNG" "MNG" "MNG" "MNG" "MOZ" "MOZ" "MOZ"
#> [1057] "MOZ" "MOZ" "MOZ" "MOZ" "MOZ" "MOZ" "MRT" "MRT" "MRT" "MRT" "MRT"
#> [1068] "MRT" "MRT" "MRT" "MRT" "MUS" "MUS" "MUS" "MUS" "MUS" "MUS" "MUS"
#> [1079] "MUS" "MUS" "MWI" "MWI" "MWI" "MWI" "MWI" "MWI" "MWI" "MWI" "MWI"
#> [1090] "MYS" "MYS" "MYS" "MYS" "MYS" "MYS" "MYS" "MYS" "MYS" "NAM" "NAM"
#> [1101] "NAM" "NAM" "NAM" "NAM" "NAM" "NAM" "NAM" "NER" "NER" "NER" "NER"
#> [1112] "NER" "NER" "NER" "NER" "NER" "NGA" "NGA" "NGA" "NGA" "NGA" "NGA"
#> [1123] "NGA" "NGA" "NGA" "NIC" "NIC" "NIC" "NIC" "NIC" "NIC" "NIC" "NIC"
#> [1134] "NIC" "NIU" "NIU" "NIU" "NIU" "NIU" "NIU" "NIU" "NIU" "NIU" "NLD"
#> [1145] "NLD" "NLD" "NLD" "NLD" "NLD" "NLD" "NLD" "NLD" "NOR" "NOR" "NOR"
#> [1156] "NOR" "NOR" "NOR" "NOR" "NOR" "NOR" "NPL" "NPL" "NPL" "NPL" "NPL"
#> [1167] "NPL" "NPL" "NPL" "NPL" "NRU" "NRU" "NRU" "NRU" "NRU" "NRU" "NRU"
#> [1178] "NRU" "NRU" "NZL" "NZL" "NZL" "NZL" "NZL" "NZL" "NZL" "NZL" "NZL"
#> [1189] "OMN" "OMN" "OMN" "OMN" "OMN" "OMN" "OMN" "OMN" "OMN" "PAK" "PAK"
#> [1200] "PAK" "PAK" "PAK" "PAK" "PAK" "PAK" "PAK" "PAN" "PAN" "PAN" "PAN"
#> [1211] "PAN" "PAN" "PAN" "PAN" "PAN" "PER" "PER" "PER" "PER" "PER" "PER"
#> [1222] "PER" "PER" "PER" "PHL" "PHL" "PHL" "PHL" "PHL" "PHL" "PHL" "PHL"
#> [1233] "PHL" "PLW" "PLW" "PLW" "PLW" "PLW" "PLW" "PLW" "PLW" "PLW" "PNG"
#> [1244] "PNG" "PNG" "PNG" "PNG" "PNG" "PNG" "PNG" "PNG" "POL" "POL" "POL"
#> [1255] "POL" "POL" "POL" "POL" "POL" "POL" "PRK" "PRK" "PRK" "PRK" "PRK"
#> [1266] "PRK" "PRK" "PRK" "PRK" "PRT" "PRT" "PRT" "PRT" "PRT" "PRT" "PRT"
#> [1277] "PRT" "PRT" "PRY" "PRY" "PRY" "PRY" "PRY" "PRY" "PRY" "PRY" "PRY"
#> [1288] "PSE" "PSE" "PSE" "PSE" "PSE" "PSE" "PSE" "PSE" "PSE" "ROU" "ROU"
#> [1299] "ROU" "ROU" "ROU" "ROU" "ROU" "ROU" "ROU" "RUS" "RUS" "RUS" "RUS"
#> [1310] "RUS" "RUS" "RUS" "RUS" "RUS" "RWA" "RWA" "RWA" "RWA" "RWA" "RWA"
#> [1321] "RWA" "RWA" "RWA" "SAU" "SAU" "SAU" "SAU" "SAU" "SAU" "SAU" "SAU"
#> [1332] "SAU" "SDN" "SDN" "SDN" "SDN" "SDN" "SDN" "SDN" "SDN" "SDN" "SEN"
#> [1343] "SEN" "SEN" "SEN" "SEN" "SEN" "SEN" "SEN" "SEN" "SGP" "SGP" "SGP"
#> [1354] "SGP" "SGP" "SGP" "SGP" "SGP" "SGP" "SLB" "SLB" "SLB" "SLB" "SLB"
#> [1365] "SLB" "SLB" "SLB" "SLB" "SLE" "SLE" "SLE" "SLE" "SLE" "SLE" "SLE"
#> [1376] "SLE" "SLE" "SLV" "SLV" "SLV" "SLV" "SLV" "SLV" "SLV" "SLV" "SLV"
#> [1387] "SOM" "SOM" "SOM" "SOM" "SOM" "SOM" "SOM" "SOM" "SOM" "SRB" "SRB"
#> [1398] "SRB" "SRB" "SRB" "SRB" "SRB" "SRB" "SRB" "SSD" "SSD" "SSD" "SSD"
#> [1409] "SSD" "SSD" "SSD" "SSD" "SSD" "STP" "STP" "STP" "STP" "STP" "STP"
#> [1420] "STP" "STP" "STP" "SUR" "SUR" "SUR" "SUR" "SUR" "SUR" "SUR" "SUR"
#> [1431] "SUR" "SVK" "SVK" "SVK" "SVK" "SVK" "SVK" "SVK" "SVK" "SVK" "SVN"
#> [1442] "SVN" "SVN" "SVN" "SVN" "SVN" "SVN" "SVN" "SVN" "SWE" "SWE" "SWE"
#> [1453] "SWE" "SWE" "SWE" "SWE" "SWE" "SWE" "SWZ" "SWZ" "SWZ" "SWZ" "SWZ"
#> [1464] "SWZ" "SWZ" "SWZ" "SWZ" "SYC" "SYC" "SYC" "SYC" "SYC" "SYC" "SYC"
#> [1475] "SYC" "SYC" "SYR" "SYR" "SYR" "SYR" "SYR" "SYR" "SYR" "SYR" "SYR"
#> [1486] "TCD" "TCD" "TCD" "TCD" "TCD" "TCD" "TCD" "TCD" "TCD" "TGO" "TGO"
#> [1497] "TGO" "TGO" "TGO" "TGO" "TGO" "TGO" "TGO" "THA" "THA" "THA" "THA"
#> [1508] "THA" "THA" "THA" "THA" "THA" "TJK" "TJK" "TJK" "TJK" "TJK" "TJK"
#> [1519] "TJK" "TJK" "TJK" "TKM" "TKM" "TKM" "TKM" "TKM" "TKM" "TKM" "TKM"
#> [1530] "TKM" "TLS" "TLS" "TLS" "TLS" "TLS" "TLS" "TLS" "TLS" "TLS" "TON"
#> [1541] "TON" "TON" "TON" "TON" "TON" "TON" "TON" "TON" "TTO" "TTO" "TTO"
#> [1552] "TTO" "TTO" "TTO" "TTO" "TTO" "TTO" "TUN" "TUN" "TUN" "TUN" "TUN"
#> [1563] "TUN" "TUN" "TUN" "TUN" "TUR" "TUR" "TUR" "TUR" "TUR" "TUR" "TUR"
#> [1574] "TUR" "TUR" "TUV" "TUV" "TUV" "TUV" "TUV" "TUV" "TUV" "TUV" "TUV"
#> [1585] "TZA" "TZA" "TZA" "TZA" "TZA" "TZA" "TZA" "TZA" "TZA" "UGA" "UGA"
#> [1596] "UGA" "UGA" "UGA" "UGA" "UGA" "UGA" "UGA" "UKR" "UKR" "UKR" "UKR"
#> [1607] "UKR" "UKR" "UKR" "UKR" "UKR" "UNK" "UNK" "UNK" "UNK" "UNK" "UNK"
#> [1618] "UNK" "UNK" "UNK" "URY" "URY" "URY" "URY" "URY" "URY" "URY" "URY"
#> [1629] "URY" "USA" "USA" "USA" "USA" "USA" "USA" "USA" "USA" "USA" "UZB"
#> [1640] "UZB" "UZB" "UZB" "UZB" "UZB" "UZB" "UZB" "UZB" "VCT" "VCT" "VCT"
#> [1651] "VCT" "VCT" "VCT" "VCT" "VCT" "VCT" "VEN" "VEN" "VEN" "VEN" "VEN"
#> [1662] "VEN" "VEN" "VEN" "VEN" "VNM" "VNM" "VNM" "VNM" "VNM" "VNM" "VNM"
#> [1673] "VNM" "VNM" "VUT" "VUT" "VUT" "VUT" "VUT" "VUT" "VUT" "VUT" "VUT"
#> [1684] "WSM" "WSM" "WSM" "WSM" "WSM" "WSM" "WSM" "WSM" "WSM" "YEM" "YEM"
#> [1695] "YEM" "YEM" "YEM" "YEM" "YEM" "YEM" "YEM" "ZAF" "ZAF" "ZAF" "ZAF"
#> [1706] "ZAF" "ZAF" "ZAF" "ZAF" "ZAF" "ZMB" "ZMB" "ZMB" "ZMB" "ZMB" "ZMB"
#> [1717] "ZMB" "ZMB" "ZMB" "ZWE" "ZWE" "ZWE" "ZWE" "ZWE" "ZWE" "ZWE" "ZWE"
#> [1728] "ZWE"
```

This is now a plain old vector, so it can be indexed with single square brackets:

```
data[[1]][1]
#> [1] "AFG"
```

But that too is a vector, so it can of course be indexed as well (for some value of “of course”):

```
data[[1]][1][1]
#> [1] "AFG"
```

Thus,
`data[1][[1]]`

produces a tibble,
then selects the first column vector from it,
so it still gives us a vector.
*This is not madness.*
It is merely…differently sane.

What is the average estimate? We start by grabbing that column for convenience:

```
estimates = data.estimate
print(len(estimates))
#> 1728
```

```
print(estimates.mean())
#> 0.3870192307692308
```

This translates almost directly to R:

```
estimates <- data$estimate
length(estimates)
#> [1] 1728
```

```
mean(estimates)
#> [1] NA
```

It seems that the void is always there, waiting for us… Let’s fix this in R first:

```
mean(estimates, na.rm=TRUE)
#> [1] 0.3870192
```

And then try to get the statistically correct behavior in Pandas:

```
print(estimates.mean(skipna=False))
#> nan
```

Many functions in R use `na.rm`

to control whether `NA`

s are removed or not.
(Remember, the `.`

character is just another part of the name)
R’s default behavior is to leave `NA`

s in, and then to include them in aggregate computations.
Python’s is to get rid of missing values early and work with what’s left,
which makes translating code from one language to the next much more interesting than it might otherwise be.
But other than that, the statistics works the same way in Python:

```
print(estimates.min())
#> 0.0
```

```
print(estimates.max())
#> 0.95
```

```
print(estimates.std())
#> 0.3034511074214113
```

Here are the equivalent computations in R:

```
min(estimates, na.rm=TRUE)
#> [1] 0
```

```
max(estimates, na.rm=TRUE)
#> [1] 0.95
```

```
sd(estimates, na.rm=TRUE)
#> [1] 0.3034511
```

A good use of aggregation is to check the quality of the data. For example, we can ask if there are any records where some of the estimate, the low value, or the high value are missing, but not all of them:

```
print((data.hi.isnull() != data.lo.isnull()).any())
#> False
```

```
any(is.na(data$hi) != is.na(data$lo))
#> [1] FALSE
```

By “filtering”, we mean “selecting records by value”.
As discussed earlier,
the simplest approach is to use a vector of logical values to keep only the values corresponding to `TRUE`

.
In Python, this is:

```
maximal = estimates[estimates >= 0.95]
print(len(maximal))
#> 52
```

And in R:

```
maximal <- estimates[estimates >= 0.95]
length(maximal)
#> [1] 1052
```

The difference is unexpected. Let’s have a closer look at the result in Python:

```
print(maximal)
#> 180 0.95
#> 181 0.95
#> 182 0.95
#> 183 0.95
#> 184 0.95
#> 185 0.95
#> 187 0.95
#> 360 0.95
#> 361 0.95
#> 362 0.95
#> 379 0.95
#> 380 0.95
#> 381 0.95
#> 382 0.95
#> 384 0.95
#> 385 0.95
#> 386 0.95
#> 446 0.95
#> 447 0.95
#> 461 0.95
#> 792 0.95
#> 793 0.95
#> 794 0.95
#> 795 0.95
#> 796 0.95
#> 797 0.95
#> 910 0.95
#> 911 0.95
#> 954 0.95
#> 955 0.95
#> 956 0.95
#> 957 0.95
#> 958 0.95
#> 959 0.95
#> 960 0.95
#> 961 0.95
#> 962 0.95
#> 1097 0.95
#> 1106 0.95
#> 1127 0.95
#> 1428 0.95
#> 1429 0.95
#> 1461 0.95
#> 1553 0.95
#> 1603 0.95
#> 1606 0.95
#> 1624 0.95
#> 1625 0.95
#> 1626 0.95
#> 1628 0.95
#> 1707 0.95
#> 1709 0.95
#> Name: estimate, dtype: float64
```

And in R:

```
maximal
#> [1] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [14] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [27] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [40] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [53] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [66] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [79] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [92] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [105] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [118] NA NA NA NA NA NA NA 0.95 0.95 0.95 0.95 0.95 0.95
#> [131] 0.95 NA NA NA NA NA NA NA NA NA NA NA NA
#> [144] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [157] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [170] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [183] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [196] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [209] 0.95 0.95 0.95 0.95 0.95 0.95 0.95 0.95 0.95 0.95 NA NA NA
#> [222] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [235] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [248] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [261] NA NA NA NA NA 0.95 0.95 NA NA 0.95 NA NA NA
#> [274] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [287] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [300] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [313] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [326] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [339] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [352] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [365] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [378] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [391] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [404] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [417] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [430] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [443] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [456] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [469] NA NA NA 0.95 0.95 0.95 0.95 0.95 0.95 NA NA NA NA
#> [482] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [495] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [508] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [521] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [534] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [547] NA NA 0.95 0.95 NA NA NA NA NA NA NA NA NA
#> [560] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [573] NA NA NA NA NA 0.95 0.95 0.95 0.95 0.95 0.95 0.95 0.95
#> [586] 0.95 NA NA NA NA NA NA NA NA NA NA NA NA
#> [599] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [612] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [625] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [638] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [651] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [664] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [677] NA 0.95 NA 0.95 NA NA NA 0.95 NA NA NA NA NA
#> [690] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [703] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [716] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [729] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [742] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [755] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [768] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [781] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [794] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [807] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [820] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [833] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [846] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [859] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [872] NA NA NA 0.95 0.95 NA NA NA NA NA NA NA NA
#> [885] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [898] NA NA NA NA NA NA NA 0.95 NA NA NA NA NA
#> [911] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [924] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [937] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [950] NA NA NA NA NA NA 0.95 NA NA NA NA NA NA
#> [963] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [976] NA 0.95 0.95 NA NA NA NA NA NA NA NA NA NA
#> [989] 0.95 0.95 0.95 0.95 NA NA NA NA NA NA NA NA NA
#> [1002] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [1015] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [1028] NA NA NA NA NA NA NA NA NA NA NA NA NA
#> [1041] NA NA NA NA NA NA NA NA NA 0.95 0.95 NA
```

It appears that R has kept the unknown values in order to highlight just how little we know—just how little
we *can* know.
More precisely,
wherever there was an `NA`

in the original data
there is an `NA`

in the logical vector
and hence an `NA`

in the final vector.
Let us then turn to `which`

to get a vector of indices at which a vector contains `TRUE`

.
This function does not return indices for `FALSE`

or `NA`

:

```
which(estimates >= 0.95)
#> [1] 181 182 183 184 185 186 188 361 362 363 380 381 382 383
#> [15] 385 386 387 447 448 462 793 794 795 796 797 798 911 912
#> [29] 955 956 957 958 959 960 961 962 963 1098 1107 1128 1429 1430
#> [43] 1462 1554 1604 1607 1625 1626 1627 1629 1708 1710
```

And as a quick check:

```
length(which(estimates >= 0.95))
#> [1] 52
```

So now we can index our vector with the result of the `which`

:

```
maximal <- estimates[which(estimates >= 0.95)]
maximal
#> [1] 0.95 0.95 0.95 0.95 0.95 0.95 0.95 0.95 0.95 0.95 0.95 0.95 0.95 0.95
#> [15] 0.95 0.95 0.95 0.95 0.95 0.95 0.95 0.95 0.95 0.95 0.95 0.95 0.95 0.95
#> [29] 0.95 0.95 0.95 0.95 0.95 0.95 0.95 0.95 0.95 0.95 0.95 0.95 0.95 0.95
#> [43] 0.95 0.95 0.95 0.95 0.95 0.95 0.95 0.95 0.95 0.95
```

But should we do this?
Those `NA`

s are important information,
and should not be discarded so blithely.
What we should *really* be doing is using the tools the tidyverse provides
rather than clever indexing tricks.
These behave consistently across a wide scale of problems
and encourage use of patterns that make it easier for others to understand our programs.

The five basic data transformation operations in the tidyverse are:

`filter`

: choose observations (rows) by value(s)`arrange`

: reorder rows`select`

: choose variables (columns) by name`mutate`

: derive new variables from existing ones`summarize`

: combine many values to create a single new value

`filter(tibble, ...criteria...)`

keeps rows that pass all of the specified criteria:

```
filter(data, lo > 0.5)
#> # A tibble: 183 x 5
#> country year estimate hi lo
#> <chr> <int> <dbl> <dbl> <dbl>
#> 1 ARG 2016 0.67 0.77 0.61
#> 2 ARG 2017 0.66 0.77 0.6
#> 3 AZE 2014 0.74 0.95 0.53
#> 4 AZE 2015 0.83 0.95 0.64
#> 5 AZE 2016 0.75 0.95 0.56
#> 6 AZE 2017 0.74 0.95 0.56
#> 7 BLR 2009 0.95 0.95 0.95
#> 8 BLR 2010 0.95 0.95 0.95
#> 9 BLR 2011 0.95 0.95 0.91
#> 10 BLR 2012 0.95 0.95 0.95
#> # … with 173 more rows
```

Notice that the expression is `lo > 0.5`

rather than `"lo" > 0.5`

.
The latter expression returns the entire table
because the string `"lo"`

is greater than the number 0.5 everywhere.
But wait:
how is it that `lo`

can be used on its own?
It is the name of a column, but there is no variable called `lo`

.

The answer is that R uses lazy evaluation of arguments.
Arguments aren’t evaluated until they’re needed,
so the function `filter`

actually gets the expression `lo > 0.5`

,
which allows it to check that there’s a column called `lo`

and then use it appropriately.
This is much tidier than `filter(data, data$lo > 0.5)`

or `filter(data, "lo > 0.5")`

,
and is *not* some kind of eldritch wizardry.
Many languages rely on lazy evaluation,
and when used circumspectly,
it allows us to produce code that is easier to read.

But we can do even better by using the pipe operator `%>%`

,
which is about to become your new best friend:

```
data %>% filter(lo > 0.5)
#> # A tibble: 183 x 5
#> country year estimate hi lo
#> <chr> <int> <dbl> <dbl> <dbl>
#> 1 ARG 2016 0.67 0.77 0.61
#> 2 ARG 2017 0.66 0.77 0.6
#> 3 AZE 2014 0.74 0.95 0.53
#> 4 AZE 2015 0.83 0.95 0.64
#> 5 AZE 2016 0.75 0.95 0.56
#> 6 AZE 2017 0.74 0.95 0.56
#> 7 BLR 2009 0.95 0.95 0.95
#> 8 BLR 2010 0.95 0.95 0.95
#> 9 BLR 2011 0.95 0.95 0.91
#> 10 BLR 2012 0.95 0.95 0.95
#> # … with 173 more rows
```

This may not seem like much of an improvement,
but neither does a Unix pipe consisting of `cat filename.txt | head`

.
What about this?

```
filter(data, (estimate != 0.95) & (lo > 0.5) & (hi <= (lo + 0.1)))
#> # A tibble: 1 x 5
#> country year estimate hi lo
#> <chr> <int> <dbl> <dbl> <dbl>
#> 1 TTO 2017 0.94 0.95 0.86
```

It uses the vectorized “and” operator `&`

twice,
and parsing the condition takes a human being at least a few seconds.
Its tidyverse equivalent is:

```
data %>% filter(estimate != 0.95) %>% filter(lo > 0.5) %>% filter(hi <= (lo + 0.1))
#> # A tibble: 1 x 5
#> country year estimate hi lo
#> <chr> <int> <dbl> <dbl> <dbl>
#> 1 TTO 2017 0.94 0.95 0.86
```

Breaking the condition into stages like this doesn’t always make reading easier, but it often helps development and testing.

Let’s increase the band from 10% to 20%:

```
data %>% filter(estimate != 0.95) %>% filter(lo > 0.5) %>% filter(hi <= (lo + 0.2))
#> # A tibble: 55 x 5
#> country year estimate hi lo
#> <chr> <int> <dbl> <dbl> <dbl>
#> 1 ARG 2016 0.67 0.77 0.61
#> 2 ARG 2017 0.66 0.77 0.6
#> 3 CHL 2011 0.64 0.72 0.56
#> 4 CHL 2013 0.67 0.77 0.59
#> 5 CHL 2014 0.77 0.87 0.67
#> 6 CHL 2015 0.92 0.95 0.79
#> 7 CHL 2016 0.7 0.79 0.62
#> 8 CHL 2017 0.85 0.95 0.76
#> 9 CPV 2014 0.94 0.95 0.76
#> 10 CPV 2016 0.94 0.95 0.76
#> # … with 45 more rows
```

And then order by `lo`

in descending order,
breaking the line the way the tidyverse style guide recommends:

```
data %>%
filter(estimate != 0.95) %>%
filter(lo > 0.5) %>%
filter(hi <= (lo + 0.2)) %>%
arrange(desc(lo))
#> # A tibble: 55 x 5
#> country year estimate hi lo
#> <chr> <int> <dbl> <dbl> <dbl>
#> 1 TTO 2017 0.94 0.95 0.86
#> 2 SWZ 2011 0.93 0.95 0.84
#> 3 CUB 2014 0.92 0.95 0.83
#> 4 TTO 2016 0.9 0.95 0.83
#> 5 CRI 2009 0.92 0.95 0.81
#> 6 CRI 2012 0.89 0.95 0.81
#> 7 NAM 2014 0.91 0.95 0.81
#> 8 URY 2016 0.9 0.95 0.81
#> 9 ZMB 2014 0.91 0.95 0.81
#> 10 KAZ 2015 0.84 0.95 0.8
#> # … with 45 more rows
```

We can now select the three columns we care about:

```
data %>%
filter(estimate != 0.95) %>%
filter(lo > 0.5) %>%
filter(hi <= (lo + 0.2)) %>%
arrange(desc(lo)) %>%
select(year, lo, hi)
#> # A tibble: 55 x 3
#> year lo hi
#> <int> <dbl> <dbl>
#> 1 2017 0.86 0.95
#> 2 2011 0.84 0.95
#> 3 2014 0.83 0.95
#> 4 2016 0.83 0.95
#> 5 2009 0.81 0.95
#> 6 2012 0.81 0.95
#> 7 2014 0.81 0.95
#> 8 2016 0.81 0.95
#> 9 2014 0.81 0.95
#> 10 2015 0.8 0.95
#> # … with 45 more rows
```

Once again,
we are using the unquoted column names `year`

, `lo`

, and `hi`

and letting R’s lazy evaluation take care of the details for us.

Rather than selecting these three columns,
we can select *out* the columns we’re not interested in by negating their names.
This leaves the columns that are kept in their original order,
rather than putting `lo`

before `hi`

,
which won’t matter if we later select by name,
but *will* if we ever want to select by position:

```
data %>%
filter(estimate != 0.95) %>%
filter(lo > 0.5) %>%
filter(hi <= (lo + 0.2)) %>%
arrange(desc(lo)) %>%
select(-country, -estimate)
#> # A tibble: 55 x 3
#> year hi lo
#> <int> <dbl> <dbl>
#> 1 2017 0.95 0.86
#> 2 2011 0.95 0.84
#> 3 2014 0.95 0.83
#> 4 2016 0.95 0.83
#> 5 2009 0.95 0.81
#> 6 2012 0.95 0.81
#> 7 2014 0.95 0.81
#> 8 2016 0.95 0.81
#> 9 2014 0.95 0.81
#> 10 2015 0.95 0.8
#> # … with 45 more rows
```

Giddy with power,
we now add a column containing the difference between the low and high values.
This can be done using either `mutate`

,
which adds new columns to the end of an existing tibble,
or with `transmute`

,
which creates a new tibble containing only the columns we explicitly ask for.
Since we want to keep `hi`

and `lo`

,
we decide to use `mutate`

:

```
data %>%
filter(estimate != 0.95) %>%
filter(lo > 0.5) %>%
filter(hi <= (lo + 0.2)) %>%
arrange(desc(lo)) %>%
select(-country, -estimate) %>%
mutate(difference = hi - lo)
#> # A tibble: 55 x 4
#> year hi lo difference
#> <int> <dbl> <dbl> <dbl>
#> 1 2017 0.95 0.86 0.0900
#> 2 2011 0.95 0.84 0.110
#> 3 2014 0.95 0.83 0.12
#> 4 2016 0.95 0.83 0.12
#> 5 2009 0.95 0.81 0.140
#> 6 2012 0.95 0.81 0.140
#> 7 2014 0.95 0.81 0.140
#> 8 2016 0.95 0.81 0.140
#> 9 2014 0.95 0.81 0.140
#> 10 2015 0.95 0.8 0.150
#> # … with 45 more rows
```

Does the difference between high and low estimates vary by year?
To answer that question,
we use `group_by`

to group records by value
and then `summarize`

to aggregate within groups.
We might as well get rid of the `arrange`

and `select`

calls in our pipeline at this point,
since we’re not using them,
and count how many records contributed to each aggregation using `n()`

:

```
data %>%
filter(estimate != 0.95) %>%
filter(lo > 0.5) %>%
filter(hi <= (lo + 0.2)) %>%
mutate(difference = hi - lo) %>%
group_by(year) %>%
summarize(n(), mean(year))
#> # A tibble: 9 x 3
#> year `n()` `mean(year)`
#> <int> <int> <dbl>
#> 1 2009 3 2009
#> 2 2010 3 2010
#> 3 2011 5 2011
#> 4 2012 5 2012
#> 5 2013 6 2013
#> 6 2014 10 2014
#> 7 2015 6 2015
#> 8 2016 10 2016
#> 9 2017 7 2017
```

Let’s do that again with more meaningful names for the final table’s columns:

```
data %>%
filter(estimate != 0.95) %>%
filter(lo > 0.5) %>%
filter(hi <= (lo + 0.2)) %>%
mutate(difference = hi - lo) %>%
group_by(year) %>%
summarize(count = n(), ave_diff = mean(year))
#> # A tibble: 9 x 3
#> year count ave_diff
#> <int> <int> <dbl>
#> 1 2009 3 2009
#> 2 2010 3 2010
#> 3 2011 5 2011
#> 4 2012 5 2012
#> 5 2013 6 2013
#> 6 2014 10 2014
#> 7 2015 6 2015
#> 8 2016 10 2016
#> 9 2017 7 2017
```

(We could also add a call to `rename`

,
but for small tables like this,
setting column names on the fly is perfectly comprehensible.)

Now,
how might we do this with Pandas?
On approach is to use a single multi-part `.query`

to select data
and store the result in a variable so that we can refer to the `hi`

and `lo`

columns twice
without repeating the filtering expression.
We then group by year and aggregate, again using strings for column names:

```
data = pd.read_csv('tidy/infant_hiv.csv')
data = data.query('(estimate != 0.95) & (lo > 0.5) & (hi <= (lo + 0.2))')
data = data.assign(difference = (data.hi - data.lo))
grouped = data.groupby('year').agg({'difference' : {'ave_diff' : 'mean', 'count' : 'count'}})
#> /Users/gvwilson/anaconda3/lib/python3.6/site-packages/pandas/core/groupby/groupby.py:4658: FutureWarning: using a dict with renaming is deprecated and will be removed in a future version
#> return super(DataFrameGroupBy, self).aggregate(arg, *args, **kwargs)
print(grouped)
#> difference
#> ave_diff count
#> year
#> 2009 0.170000 3
#> 2010 0.186667 3
#> 2011 0.168000 5
#> 2012 0.186000 5
#> 2013 0.183333 6
#> 2014 0.168000 10
#> 2015 0.161667 6
#> 2016 0.166000 10
#> 2017 0.152857 7
```

There are other ways to tackle this problem with Pandas, but the tidyverse approach produces code that I find more readable.

`install.packages('name')`

installs packages.`library(name)`

(without quoting the name) loads a package.`library(tidyverse)`

loads the entire collection of tidyverse libraries at once.`read_csv(filename)`

reads CSV files that use the string ‘NA’ to represent missing values.`read_csv`

infers each column’s data types based on the first thousand values it reads.- A tibble is the tidyverse’s version of a data frame, which represents tabular data.
`head(tibble)`

and`tail(tibble)`

inspect the first and last few rows of a tibble.`summary(tibble)`

displays a summary of a tibble’s structure and values.`tibble$column`

selects a column from a tibble, returning a vector as a result.`tibble['column']`

selects a column from a tibble, returning a tibble as a result.`tibble[,c]`

selects column`c`

from a tibble, returning a tibble as a result.`tibble[r,]`

selects row`r`

from a tibble, returning a tibble as a result.- Use ranges and logical vectors as indices to select multiple rows/columns or specific rows/columns from a tibble.
`tibble[[c]]`

selects column`c`

from a tibble, returning a vector as a result.`min(...)`

,`mean(...)`

,`max(...)`

, and`std(...)`

calculates the minimum, mean, maximum, and standard deviation of data.- These aggregate functions include
`NA`

s in their calculations, and so will produce`NA`

if the input data contains any. - Use
`func(data, na.rm = TRUE)`

to remove`NA`

s from data before calculations are done (but make sure this is statistically justified). `filter(tibble, condition)`

selects rows from a tibble that pass a logical test on their values.`arrange(tibble, column)`

or`arrange(desc(column))`

arrange rows according to values in a column (the latter in descending order).`select(tibble, column, column, ...)`

selects columns from a tibble.`select(tibble, -column)`

selects*out*a column from a tibble.`mutate(tibble, name = expression, name = expression, ...)`

adds new columns to a tibble using values from existing columns.`group_by(tibble, column, column, ...)`

groups rows that have the same values in the specified columns.`summarize(tibble, name = expression, name = expression)`

aggregates tibble values (by groups if the rows have been grouped).`tibble %>% function(arguments)`

performs the same operation as`function(tibble, arguments)`

.- Use
`%>%`

to create pipelines in which the left side of each`%>%`

becomes the first argument of the next stage.