7 R Tips Rescued from the Vault

23 September 2013

I keep a 2000-lines long file full of R commands that I considered worthy of remembering at some point during the past 5 years. Life is too short, so here are 7 tips that don’t get enough publicity, ranked from most to least awesome.

Use “.” to repeat the last returned value

This one is so useful, it should come enabled by default in every R installation. Stick this line in your ~/.Rprofile

makeActiveBinding(".", function() .Last.value, .GlobalEnv)

Now open a new R console, and type:

# let's say you forgot to save some calculation in a variable.
rnorm(20)

# Now you can just use "."
a <- .

length(a) # 20

Save objects into variables

Use saveRDS and readRDS instead of save and load, so you can read from, and write to, objects with different names.

a <- rnorm(1e5)
saveRDS(a, file="my_object.rds")

b <- readRDS("my_object.rds")

Get the arguments used by a function

# I used to do this to quickly look up the usage of a function
head(read.csv)

# but this is better
args(read.csv)
# function (file, header = TRUE, sep = ",", quote = "\"", dec = ".",
#     fill = TRUE, comment.char = "", ...)
# NULL

Add names to a vector in one step

# instead of
tmp <- 1:3
names(tmp) <-  c("foo", "bar", "baz")

# use setNames()
tmp <- setNames(1:3, c("foo", "bar", "baz"))

Store meta information using attributes

a <- data.frame(x = 1:3, y = 4:6)
attr(a, "experiment_id") <- "exp_1"

# you can still use the object like you normally would
a
# but you can also easily access is related information
attr(a, "experiment_id") # exp_1

# you can also initialize multiple attributes at once
# but realize that it overwrites whatever arguments you had previously set
attributes(a) <- list(sample_number = 1, sample_id = "ABC")

attributes(a)
# $sample_number
#  [1] 1
# $sample_id
#  [1] "ABC"

Paginate long objects or files

It works just like Unix’s less command, so you can move up and down with the arrow keys, the space bar, shift g and gg to advance a move line by line, screen by screen, go to the end, or back to the beginning, respectively.

page(rnorm(1e5))

Ensure that functions only accept a limited set of arguments

# Only "A" and "B" are allowed
a <-function(x, y = c("A","B")){
  y <- match.arg(y)
  y
}
a() # y equals "A"
a(3,"A") # y equals "A"
a(3,"B") # y equals "B"
a(3,"C") # Error in match.arg(y) : 'arg' should be one of “A”, “B”