Apply a Function over a List or Vector
lapply returns a list of the same length as
element of which is the result of applying
FUN to the
corresponding element of
sapply is a user-friendly version and wrapper of
by default returning a vector, matrix or, if
simplify = "array", an
array if appropriate, by applying
sapply(x, f, simplify = FALSE, USE.NAMES = FALSE) is the same as
vapply is similar to
sapply, but has a pre-specified
type of return value, so it can be safer (and sometimes faster) to
replicate is a wrapper for the common use of
repeated evaluation of an expression (which will usually involve
random number generation).
simplify2array() is the utility called from
simplify is not false and is similarly called from
lapply(X, FUN, …)
sapply(X, FUN, …, simplify = TRUE, USE.NAMES = TRUE)
vapply(X, FUN, FUN.VALUE, …, USE.NAMES = TRUE)
replicate(n, expr, simplify = "array")
simplify2array(x, higher = TRUE)
- a vector (atomic or list) or an
expressionobject. Other objects (including classed objects) will be coerced by
- the function to be applied to each element of
X: see ‘Details’. In the case of functions like
%*%, the function name must be backquoted or quoted.
- optional arguments to
- logical or character string; should the result be
simplified to a vector, matrix or higher dimensional array if
sapplyit must be named and not abbreviated. The default value,
TRUE, returns a vector or matrix if appropriate, whereas if
simplify = "array"the result may be an
arrayof “rank” (\(=\)
length(dim(.))) one higher than the result of
- logical; if
Xis character, use
namesfor the result unless it had names already. Since this argument follows
…its name cannot be abbreviated.
- a (generalized) vector; a template for the return value from FUN. See ‘Details’.
- integer: the number of replications.
- the expression (a language object, usually a call) to evaluate repeatedly.
- a list, typically returned from
- logical; if true,
simplify2array()will produce a (“higher rank”) array when appropriate, whereas
higher = FALSEwould return a matrix (or vector) only. These two cases correspond to
sapply(*, simplify = "array")or
simplify = TRUE, respectively.
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
FUN must be able to accept as input any of the
X. If the latter is an atomic vector,
will always be passed a length-one vector of the same type as
X. Arguments in
… cannot have the same name as any of the
other arguments, and care may be needed to avoid partial matching to
FUN. In general-purpose code it is good practice to name the
first two arguments
… is passed
through: this both avoids partial matching to
FUN and ensures
that a sensible error message is given if arguments named
FUN are passed through
…. Simplification in
sapply is only attempted if
length greater than zero and if the return values from all elements
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. Simplification is always done in
vapply. This function
checks that all values of
FUN are compatible with the
FUN.VALUE, in that they must have the same length and type.
(Types may be promoted to a higher type within the ordering logical
< integer < double < complex, but not demoted.) Users of S4 classes should pass a list to
vapply: the internal coercion is done by the
the base namespace and not one defined by a user (e.g., by setting S4
methods on the base function).
vapply are primitive functions.
sapply(simplify = FALSE) and
replicate(simplify = FALSE), a list. For
sapply(simplify = TRUE) and
X has length zero or
n = 0, an empty list.
Otherwise an atomic vector or matrix or list of the same length as
X (of length
replicate). If simplification
occurs, the output type is determined from the highest type of the
return values in the hierarchy NULL < raw < logical < integer < double <
complex < character < list < expression, after coercion of pairlists
vapply returns a vector or array of type matching the
length(FUN.VALUE) == 1 a
vector of the same length as
X is returned, otherwise
an array. If
FUN.VALUE is not an
result is a matrix with
length(FUN.VALUE) rows and
length(X) columns, otherwise an array
dim(a) == c(dim(FUN.VALUE), length(X)). The (Dim)names of the array value are taken from the
if it is named, otherwise from the result of the first function call.
Column names of the matrix or more generally the names of the last
dimension of the array value or names of the vector value are set from
X as in
sapply(*, simplify = FALSE, USE.NAMES = FALSE) is
lapply(*). For historical reasons, the calls created by
unevaluated, and code has been written (e.g.,
relies on this. This means that the recorded call is always of the
FUN(X[[i]], ...), with
i replaced by the current
(integer or double) index. This is not normally a problem, but it can
match.call or if it is a primitive function that makes
use of the call. This means that it is often safer to call primitive
functions with a wrapper, so that e.g.
is.numeric(x)) is required to ensure that method dispatch for
is.numeric occurs correctly. If
expr is a function call, be aware of assumptions about where
it is evaluated, and in particular what
… might refer to.
You can pass additional named arguments to a function call as
additional named arguments to
replicate: see ‘Examples’.
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.
require(stats); require(graphics) 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) vapply(i39, fivenum, c(Min. = 0, "1st Qu." = 0, Median = 0, "3rd Qu." = 0, Max. = 0)) ## sapply(*, "array") -- artificial example (v <- structure(10*(5:8), names = LETTERS[1:4])) f2 <- function(x, y) outer(rep(x, length.out = 3), y) (a2 <- sapply(v, f2, y = 2*(1:5), simplify = "array")) a.2 <- vapply(v, f2, outer(1:3, 1:5), y = 2*(1:5)) stopifnot(dim(a2) == c(3,5,4), all.equal(a2, a.2), identical(dimnames(a2), list(NULL,NULL,LETTERS[1:4]))) hist(replicate(100, mean(rexp(10)))) ## use of replicate() with parameters: foo <- function(x = 1, y = 2) c(x, y) # does not work: bar <- function(n, ...) replicate(n, foo(...)) bar <- function(n, x) replicate(n, foo(x = x)) bar(5, x = 3)