Apply a Function over a List or Vector

lapply {base}

R Documentation

Apply a Function over a List or Vector

Description

lapply returns a list of the same length as X, each element of which is the result of applying FUN to the corresponding element of X.

sapply is a “user-friendly” version of lapply by default returning a vector or matrix if appropriate.

replicate is a wrapper for the common use of sapply for repeated evaluation of an expression (which will usually involve random number generation).

Usage

lapply(X, FUN, ...)

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

replicate(n, expr, simplify = TRUE)

Arguments

X	a vector (atomic or list) or an expressions vector. Other objects (including classed objects) will be coerced by as.list.
FUN	the function to be applied to each element of X: see Details. In the case of functions like +, %*%, etc., the function name must be backquoted or quoted.
...	optional arguments to FUN.
simplify	logical; should the result be simplified to a vector or matrix if possible?
USE.NAMES	logical; if TRUE and if X is character, use X as names for the result unless it had names already.
n	number of replications.
expr	expression (language object, usually a call) to evaluate repeatedly.

Details

FUN is found by a call to match.fun and typically is specified as a function or a symbol (e.g. a backquoted name) or a character string specifying a function to be searched for from the environment of the call to lapply.

Function FUN must be able to accept as input any of the elements of X. If the latter is an atomic vector, FUN will always be passed a length-one vector of the same type as X.

Simplification in sapply is only attempted if X has length greater than zero and if the return values from all elements of X are all of the same (positive) length. If the common length is one the result is a vector, and if greater than one is a matrix with a column corresponding to each element of X.

The mode of the simplified answer is chosen to accommodate the modes of all the values returned by the calls to FUN: see unlist.

if X has length 0, the return value of sapply is always a 0-length list.

Note

sapply(*, simplify = FALSE, USE.NAMES = FALSE) is equivalent to lapply(*).

References

Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.

See Also

apply, tapply, mapply for applying a function to multiple arguments, and rapply for a recursive version of lapply(), eapply for applying a function to each entry in an environment.

Examples

x <- list(a = 1:10, beta = exp(-3:3), logic = c(TRUE,FALSE,FALSE,TRUE))
# compute the list mean for each list element
lapply(x,mean)
# median and quartiles for each list element
lapply(x, quantile, probs = 1:3/4)
sapply(x, quantile)
i39 <- sapply(3:9, seq) # list of vectors
sapply(i39, fivenum)

hist(replicate(100, mean(rexp(10))))