R.md

Cheat sheet for the R language

Packages

Installing packages:

install.packages('sp')

View version of installed packages:

packageVersion('sp')
packageDescription('sp')['Version']  # more verbose

# Print version information about R and attached or loaded packages.
sessionInfo()

Install package from tar file:

R CMD INSTALL /path/to/file

Install package from its source directory:

cd /path/to/project/source
Rscript -e "install.packages('$PWD', repos=NULL, type='source')"

Print list of functions in a package:

ls('package:achia')

Unload / detach library:

detach('package:sp', unload=T)

R on Mac OS X

Installation path of R versions:

/Library/Frameworks/R.framework/Versions

Creating packages

Store a variable inside a package's environment:

.AchiaEnv <- new.env()

set.workdir <- function(path) {
  assign('WORKDIR', path, envir=.AchiaEnv)
}

get.workdir <- function() {
  get('WORKDIR', envir=.AchiaEnv)
}

Scripting

Use this first line for R scripts:

#!/usr/bin/env Rscript

Ask for user input in Rscript:

cat('\n[Press Enter]\n')
foo <- scan("stdin", character(), n=1, nlines=1, quiet=TRUE)

Getting help

Get help about any R function or structure:

# documentation of the `rle` function
?rle

# documentation of the `read.csv` function
?read.csv

Objects in memory

# list objects in memory
ls()

# delete objects from memory
rm('variablename')

# delete all objects
rm(list = ls())

Navigating in the filesystem

# current working directory
getwd()

# change to another directory
setwd('/path/to/somewhere/else')

Extracting subsets from data frames

# these are the same
subset(airquality, Month == 5)
subset(airquality, airquality[,'Month'] == 5)
subset(airquality, airquality[,5] == 5)

Misc

Modulo operator:

# 5 mod 3 is 2
# 3 mod 5 is 3
i %% n