Programming with R: Reference

Key Points

Introduction to R and RStudio
  • Use RStudio to write and run R programs.

  • R has the usual arithmetic operators and mathematical functions.

  • Use <- to assign values to variables.

  • Use install.packages to install packages (libraries).

Seeking Help
  • Use help to get online help in R.

Data Structures
  • The basic data types in R are double, integer, complex, logical, and character.

  • These basic data types can be used to build larger data structures, called classes.

Subsetting Data
  • Indexing in R starts at 1, not 0.

  • Access individual values by location using [].

  • Access slices of data using [low:high].

  • Access arbitrary sets of data using [c(...)].

  • Use which to select subsets of data based on value.

Exploring Data Frames
  • Use cbind to add a new column to a dataframe.

  • Use rbind to add a new row to a dataframe.

  • Remove rows from a dataframe.

  • Use na.omit to remove rows from a dataframe with NA values.

Control Flow
  • Use if and else to make choices.

  • Use for to repeat operations.

Dataframe Manipulation with dplyr
  • Use the dplyr package to manipulate dataframes.

  • Use select to choose variables from a dataframe.

  • Use filter to choose data based on values.

  • Use group_by and summarize to work with subsets of data.

  • Use mutate to create new variables.

Creating Publication-Quality Graphics
  • Use ggplot2 to create plots.

  • Think about graphics in layers: aesthetics, geometry, statistics, scale transformation, and grouping.

Writing Data
  • Save plots from RStudio using the ‘Export’ button.

  • Use write.table to save tabular data.

Wrap Up


Introduction to R and RStudio

Seeking help

Data structures

Individual values in R must be one of 5 data types, multiple values can be grouped in data structures.

Data types

Basic data structures in R:

Remember that matrices are really atomic vectors underneath the hood, and that data.frames are really lists underneath the hood (this explains some of the weirder behaviour of R).





Data Frames

Useful functions for querying data structures:

Exploring Data Frames

Subsetting data

Control flow

Creating publication quality graphics


Functions explained

Writing data


Dataframe manipulation with dplyr

Dataframe manipulation with tidyr

Producing reports with knitr

Best practices for writing good code


A value given to a function or program when it runs. The term is often used interchangeably (and inconsistently) with parameter.
To give a value a name by associating a variable with it.
(of a function): the statements that are executed when a function runs.
A remark in a program that is intended to help human readers understand what is going on, but is ignored by the computer. Comments in Python, R, and the Unix shell start with a # character and run to the end of the line; comments in SQL start with --, and other languages have other conventions.
comma-separated values
(CSV) A common textual representation for tables in which the values in each row are separated by commas.
A character or characters used to separate individual values, such as the commas between columns in a CSV file.
Human-language text written to explain what software does, how it works, or how to use it.
floating-point number
A number containing a fractional part and an exponent. See also: integer.
for loop
A loop that is executed once for each value in some kind of set, list, or range. See also: while loop.
A subscript that specifies the location of a single value in a collection, such as a single pixel in an image.
A whole number, such as -12343. See also: floating-point number.
In R, the directory(ies) where packages are stored.
A collection of R functions, data and compiled code in a well-defined format. Packages are stored in a library and loaded using the library() function.
A variable named in the function’s declaration that is used to hold a value passed into the call. The term is often used interchangeably (and inconsistently) with argument.
return statement
A statement that causes a function to stop executing and return a value to its caller immediately.
A collection of information that is presented in a specific order.
An array’s dimensions, represented as a vector. For example, a 5×3 array’s shape is (5,3).
Short for “character string”, a sequence of zero or more characters.
syntax error
A programming error that occurs when statements are in an order or contain characters not expected by the programming language.
The classification of something in a program (for example, the contents of a variable) as a kind of number (e.g. floating-point, integer), string, or something else. In R the command typeof() is used to query a variables type.
while loop
A loop that keeps executing as long as some condition is true. See also: for loop.