Table of Contents

• apply(X, MARGIN, FUN, ...)
• lapply(X, FUN, ...)
• sapply(X, FUN, ..., simplify = TRUE, USE.NAMES = TRUE)
• replicate(n, expr, simplify = "array")
• mapply(FUN, ...)
• tapply(X, INDEX, FUN, …)
• do.call(what, args)

apply(X, MARGIN, FUN, ...) reference

• Apply FUN over subarrays.
• Consider MARGIN as columns to keep
• MARGIN can be a vector of dimension number or name.

A <- rbind(c(1, 2, 3),
           c(4, 5, 6),
           c(7, 8, 9))
dimnames(A) <- list(player = NULL, round = NULL)
A

      round
player [,1] [,2] [,3]
  [1,]    1    2    3
  [2,]    4    5    6
  [3,]    7    8    9

# 1 means the first dim, or row.
# So, to keep rows, `sum()` is applied to row elements.
# So, the result is a vector of each player's total score
apply(A, 1, sum)

[1]  6 15 24

# Player average
apply(A, "player", mean)

[1] 2 5 8

# Round average
apply(A, "round", mean)

[1] 4 5 6

lapply(X, FUN, ...) reference

sapply(X, FUN, ..., simplify = TRUE, USE.NAMES = TRUE) reference

• sapply is similar to lapply, but it simplifies the result.

l <- list(1, 2, 3)

lapply(l, function(x) x^2)

[[1]]
[1] 1

[[2]]
[1] 4

[[3]]
[1] 9

sapply(l, function(x) x^2)

[1] 1 4 9

replicate(n, expr, simplify = "array") reference

• Repeatedly evaluates expr
• Returns a vector, an array, or a list of the results

replicate(3, print("hello"))

[1] "hello"
[1] "hello"
[1] "hello"
[1] "hello" "hello" "hello"

mapply(FUN, ...) reference

Apply a function to multiple list or vector arguments

x <- c(1, 2, 3)
y <- c(4, 5, 6)
mapply(function(a, b) { a + b }, x, y)

[1] 5 7 9

tapply(X, INDEX, FUN, …) reference

• Apply a function to each cell of a ragged array(multiple groups mixed in an array)
• The combination of a vector and a labelling factor is an example of what is sometimes called a ragged array since the subclass sizes are possibly irregular.

x <- 1:5
y <- factor(c("a", "b", "a", "b", "c"))

tapply(x, y, mean)

a b c 
2 3 5

tapply(x, y, length)

a b c 
2 2 1

do.call(what, args) reference

• Call a function by its name
• Pass arguments as list

rnorm(n = 10, mean = 0, sd = 1)

 [1] -0.266621955  0.511712080 -0.728687674 -0.003757919  2.028559127
 [6]  2.063869831  2.230660146 -1.962791472  0.903502277  0.779437409

Equivalent to

do.call("rnorm", list(n = 10, mean = 0, sd = 1))

 [1]  0.04329682 -0.33890374 -0.75751409 -1.68195845  0.47877042 -0.38845015
 [7]  0.79256410  0.97123402 -0.30013421 -0.98092673