Absolute row number: the sequential index of a row in a table, regardless of what sections of the table is being displayed.
Aggregation: to combine many values into one, e.g., by summing a set of numbers or concatenating a set of strings.
Alias: to have two (or more) references to the same physical data.
Anonymous function: a function that has not been assigned a name. Anonymous functions are usually quite short, and are usually defined where they are used, e.g., as callbacks.
Attribute: a name-value pair associated with an object, used to store metadata about the object such as an array’s dimensions.
Catch (exception): to accept responsibility for handling an error or other unexpected event. R prefers “handling a condition” to “catching an exception”.
Condition: an error or other unexpected event that disrupts the normal flow of control. See also handle.
Constructor (class): a function that creates an object of a particular class. In the S3 object system, constructors are a convention rather than a requirement.
Copy-on-modify: the practice of creating a new copy of aliased data whenever there is an attempt to modify it so that each reference will believe theirs is the only one.
Double square brackets:
an index enclosed in
used to return a single value of the underlying type.
See also single square brackets.
Eager evaluation: evaluating an expression as soon as it is formed.
Empty vector: a vector that contains no elements. Empty vectors have a type such as logical or character, and are not the same as null.
Environment: a structure that stores a set of variable names and the values they refer to.
Error: the most severe type of built-in condition in R.
the process of taking a complex expression such as
and turning it into a single irreducible value.
Evaluating function: a function that takes arguments as values. Most functions are evaluating functions.
Exception: an object containing information about an error, or the condition that led to the error. R prefers “handling a condition” to “catching an exception”.
Filter: to choose a set of records according to the values they contain.
Fully qualified name:
an unambiguous name of the form
Functional programming: a style of programming in which functions transform data rather than modifying it. Functional programming relies heavily on higher-order functions.
Generic function: a collection of functions with similar purpose, each operating on a different class of data.
Global environment: the environment that holds top-level definitions in R, e.g., those written directly in the interpreter.
Group: to divide data into subsets according to some criteria while leaving records in a single structure.
Handle (a condition): to accept responsibility for handling an error or other unexpected event. R prefers “handling a condition” to “catching an exception”.
Helper (class): in S3, a function that constructs and validates an instance of a class.
Heterogeneous: potentially containing data of different types. Most vectors in R are homogeneous, but lists can be heterogeneous.
a function that takes one or more other functions as parameters.
Higher-order functions such as
map are commonly used in functional programming.
Homogeneous: containing data of only a single type. Most vectors in R are homogeneous.
Hubris: excessive pride or self-confidence. See also unit test (lack of).
ISO3 country code: a three-letter code defined by ISO 3166-1 that identifies a specific country, dependent territory, or other geopolitical entity.
Lazy evaluation: delaying evaluation of an expression until the value is actually needed (or at least until after the point where it is first encountered).
List comprehension: an expression that generates a new list from an existing one via an implicit loop.
Logical indexing: to index a vector or other structure with a vector of Booleans, keeping only the values that correspond to true values.
Message: the least severe type of built-in condition in R.
Method: an implementation of a generic function that handles objects of a specific class.
NA: a special value used to represent data that is Not Available.
Name collision: a situation in which the same name has been used in two different packages which are then used together, leading to ambiguity.
Negative selection: to specify the elements of a vector or other data structure that aren’t desired by negating their indices.
a special value used to represent a missing object.
NULL is not the same as
and neither is the same as an empty vector.
Quosure: a data structure containing an unevaluated expression and its environment.
Quoting function: a function that is passed expressions rather than the values of those expressions.
Package: a collection of code, data, and documentation that can be distributed and re-used.
%>% used to make the output of one function the input of the next.
Promise: a data structure used to record an unevaluated expression for lazy evaluation.
Raise (exception): a way of indicating that something has gone wrong in a program, or that some other unexpected event has occurred. R prefers “signalling a condition” to “raising an exception”.
an expression of the form
that is transformed a sequence of consecutive integers.
Reactive variable: a variable whose value is automatically updated when some other value or values change.
Recycle: to re-use values from a shorter vector in order to generate a sequence of the same length as a longer one.
Relative row number: the index of a row in a displayed portion of a table, which may or may not be the same as the absolut row number within the table.
Scalar: a single value of a particular type, such as 1 or “a”. Scalars don’t really exist in R; values that appear to be scalars are actually vectors of unit length.
Select: to choose entire columns from a table by name or location.
Setup (testing): code that is automatically run once before each unit test.
Signal (a condition): a way of indicating that something has gone wrong in a program, or that some other unexpected event has occurred. R prefers “signalling a condition” to “raising an exception”.
Single square brackets:
an index enclosed in
used to select a structure from another structure.
See also double square brackets.
Storage allocation: setting aside a block of memory for future use.
Teardown (testing): code that is automatically run once after each unit test.
Test fixture: the data structures, files, or other artefacts on which a unit test operates.
Test runner: a software tool that finds and runs unit tests.
Tibble: a modern replacement for R’s data frame, which stores tabular data in columns and rows, defined and used in the tidyverse.
Tidyverse: a collection of R packages for operating on tabular data in consistent ways.
Unit test: a function that tests one aspect or property of a piece of software.
Validator (class): a function that checks the consistency of an S3 object.
in a function,
the ability to take any number of arguments.
... to capture the “extra” arguments.
Vector: a sequence of values, usually of homogeneous type. Vectors are the fundamental data structure in R; scalars are actually vectors of unit length.
Vectorize: to write code so that operations are performed on entire vectors, rather than element-by-element within loops.
Warning: a built-in condition in R of middling severity.