R quick reference

The smallest R script, and the difference between print(), cat() and a value on its own line.

Numbers, integers, text, logicals, NA and NULL, class(), and converting with as.numeric() and friends.

Create vectors with c(), : and seq(), calculate on a whole vector at once, and pick elements by position or condition.

if / else, vectorized ifelse(), switch(), for over a vector, while, and next / break.

Define functions with function, default arguments, return a list, and apply a function to every element with sapply and lapply.

Named lists, data frames (tables), selecting rows and columns, sorting with order(), adding columns and aggregate().

paste and sprintf, nchar, substr, toupper, strsplit, and regular expressions with grepl, sub, gsub and regmatches.

mean, median, sd, quantile, table() for counts, correlation, summary(), and reproducible random numbers with set.seed().

Read what you type in the IDE's Input tab with readLines(file("stdin")) or scan().

Read project files with read.csv and readLines, and write results under /tmp with write.csv and writeLines.

Load your own functions from another file with source(), and which packages are available without installing.

What Run does with your script, the time limit, input, tests, and what a run cannot do.

What object not found, could not find function, non-numeric argument, subscript out of bounds and missing value where TRUE/FALSE needed mean and how to fix them.

Where to read more: An Introduction to R, the R language definition, and the help pages of every function.