A small glossary of terms used in R and data science, designed for novices who are still orienting themselves. Contributions are very welcome: please see the contribution guidelines if you would like to lend and hand, and please note that all contributors must abide by our Code of Conduct.
absolute path: A path that points to the same location in the filesystem regardless of where it's evaluated. An absolute path is the equivalent of latitude and longitude in geography. See also relative path.
aggregation function: A function that combines many values into one, such as
sum or max.
base R: FIXME
Cascading Style Sheets: A way to describe how HTML should be rendered.
character encoding: A specification of how characters are stored as bytes. The most commonly-used encoding today is UTF-8.
closure: A set of variables defined in the same scope whose existence has been preserved after that scope has ended. Closures are one of the trickiest ideas in programming.
Comma-Separated Values: A text format for tabular data in which each record is one row and fields are separated by commas. There are many minor variations, particularly around quoting of strings.
data frame: FIXME
escape sequence: A sequence of characters used to represent some other
character that would otherwise have a special meaning. For example, the escape
sequence \" is used to represent a double-quote character inside a
double-quoted string.
exception: An object that stores information about an error or other unusual event in a program. One part of a program will create and throw an exception to signal that something unexpected has happened; another part will catch it.
falsy: A horrible neologism meaning "equivalent to false". See also the equally horrible truthy.
functional programming: A style of programming in which data is transformed through successive application of functions, rather than by using control structures such as loops. Functional programming in R relies heavily on higher-order functions.
global installation: Installing a package in a location where it can be accessed by all users and projects. See also local installation.
global variable: A variable defined outside any particular function, which is therefore visible to all functions. See also local variable.
GNU Public License: A license that allows people to re-use software as long as they distribute the source of their changes.
header row: If present, the first of a CSV file that defines column names (but tragically, not their data types or units).
heterogeneous: Having mixed type. For example, an array is said to be heterogeneous if it contains a mix of numbers, character strings, and values of other types. See also homogeneous.
higher-order function: A function that operates on other functions. For
example, the higher-order function map executes a given function once on
each value in an list. Higher-order functions are heavily used in
functional programming.
homogeneous: Having a single type. For example, an array is said to be homogeneous if it contains only numbers or only character strings, but not a mix of the two.
Integrated Development Environment (IDE): FIXME
JSON: A way to represent data by combining basic values like numbers and character strings in arrays and name/value structures. The acronym stands for "JavaScript Object Notation"; unlike better-defined standards like XML, it is unencumbered by a syntax for comments or ways to define schemas.
lazy evaluation: see non-standard evaluation.
list: FIXME.
local installation: Placing a package inside a particular project so that it is only accessible within that project. See also global installation.
local variable: A variable defined inside a function which is only visible within that function. See also global variable and closure.
MIT License: A license that allows people to re-use software with no restrictions. mutation: Changing data in place, such as modifying an **element of an array or adding a record to a database.
name collision: The ambiguity that arises when two or more things in a program that have the same name are active at the same time. The call stack was invented in part to address this problem.
non-standard evaluation: FIXME.
NoSQL database: Any database that doesn't use the relational model. The awkward name comes from the fact that such databases don't use SQL as a query language.
package: FIXME
package manager: A program that does its best to keep track of the bits and bobs of software installed on a computer.
parameter: A variable whose value is passed into a function when the function is called. Some writers distinguish parameters (the variables) from arguments (the values passed in), but others use the terms in the opposite sense. It's all very confusing.
parse: To translate the text of a program or web page into a data structure in memory that the program can then manipulate.
production code: Software that is delivered to an end user. The term is used to distinguish such code from test code, deployment infrastructure, and everything else that programmers write along the way.
pseudo-random number: A value generated in a repeatable way that has the properties of being truly random.
pseudo-random number generator: A function that can generate a series of pseudo-random numbers after being initialized with a seed.
R Markdown: FIXME
raise: To signal that something unexpected or unusual has happened in a program by creating an exception and handing it to the error-handling system, which then tries to find a point in the program that will catch it.
read-evaluate-print loop: An interactive program that reads a command typed in by a user, executes it, prints the result, and then waits patiently for the next command. REPLs are often used to explore new ideas or for debugging.
regular expression: A pattern for matching text, written as text itself. Regular expressions are sometimes called "regexp", "regex", or "RE", and are as powerful as they are cryptic. See this documentation for more details.
relational database: A database that organizes information into tables, each of which has a fixed set of named fields (shown as columns) and a variable number of records (shown as rows). See also SQL.
relative path: A path whose destination is interpreted relative to some other location, such as the current directory. A relative path is the equivalent of giving directions using terms like "straight" and "left". See also absolute path.
root directory: The directory that contains everything else, directly or
indirectly. The root directory is written / (a bare forward slash).
scalar: FIXME
scope: The portion of a program within which a definition can be seen and used. See global-variable, local-variable, and closure.
script: FIXME
seed: A value used to initialize a pseudo-random number generator.
SQL: The language used for writing queries for relational databases. The term was originally an acronym for Structured Query Language.
string: A block of text in a program. The term is short for "character string".
string interpolation: The process of inserting text corresponding to specified values into a string, usually to make output human-readable.
table: A set of uniformly-formatted records in a relational database. Tables are usually drawn with rows (each of which represents one record) and columns (each of which represents a field).
tibble: FIXME
tidy data: FIXME
tidyverse: FIXME
truthy: A truly Orwellian neologism meaning "not equivalent to false". See also falsy, but only if you are able to set aside your respect for the English language.
Unicode: A standard that defines numeric codes for many thousands of characters and symbols. Unicode does not define how those numbers are stored; that is done by standards like UTF-8.
unit test: A test that exercises one property or expected behavior of a system.
UTF-8: A way to store the numeric codes representing Unicode characters in memory that is backward-compatible with the older ASCII standard.
variable: A name in a program that has some data associated with it. A variable's value can be changed after definition. See also constant.
vector: FIXME
whitespace: The space, newline, carriage return, and horizontal and vertical tab characters that take up space but don't create a visible mark. The name comes from their appearance on a printed page in the era of typewriters.