lapply
Apply a Function over a List or Vector
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 userfriendly version and wrapper of lapply
by default returning a vector, matrix or, if simplify = "array"
, an
array if appropriate, by applying simplify2array()
.
sapply(x, f, simplify = FALSE, USE.NAMES = FALSE)
is the same as
lapply(x, f)
.
vapply
is similar to sapply
, but has a prespecified
type of return value, so it can be safer (and sometimes faster) to
use.
replicate
is a wrapper for the common use of sapply
for
repeated evaluation of an expression (which will usually involve
random number generation).
simplify2array()
is the utility called from sapply()
when simplify
is not false and is similarly called from
mapply()
.
Usage
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)
Arguments
 X
 a vector (atomic or list) or an
expression
object. Other objects (including classed objects) will be coerced bybase::as.list
.  FUN
 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
FUN
.  simplify
 logical or character string; should the result be
simplified to a vector, matrix or higher dimensional array if
possible? For
sapply
it must be named and not abbreviated. The default value,TRUE
, returns a vector or matrix if appropriate, whereas ifsimplify = "array"
the result may be anarray
of “rank” ($=$length(dim(.))
) one higher than the result ofFUN(X[[i]])
.  USE.NAMES
 logical; if
TRUE
and ifX
is character, useX
asnames
for the result unless it had names already. Since this argument follows...
its name cannot be abbreviated.  FUN.VALUE
 a (generalized) vector; a template for the return value from FUN. See ‘Details’.
 n
 integer: the number of replications.
 expr
 the expression (a language object, usually a call) to evaluate repeatedly.
 x
 a list, typically returned from
lapply()
.  higher
 logical; if true,
simplify2array()
will produce a (“higher rank”) array when appropriate, whereashigher = FALSE
would return a matrix (or vector) only. These two cases correspond tosapply(*, simplify = "array")
orsimplify = TRUE
, respectively.
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 lengthone 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 generalpurpose code it is good practice to name the
first two arguments X
and FUN
if ...
is passed
through: this both avoids partial matching to FUN
and ensures
that a sensible error message is given if arguments named X
or
FUN
are passed through ...
.
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
.
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 lapply
and
vapply
: the internal coercion is done by the as.list
in
the base namespace and not one defined by a user (e.g., by setting S4
methods on the base function).
lapply
and vapply
are primitive functions.
Value

For lapply, sapply(simplify = FALSE) and
replicate(simplify = FALSE), a list.For sapply(simplify = TRUE) and replicate(simplify =
TRUE): if 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 n for 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
to lists.vapply returns a vector or array of type matching the
FUN.VALUE. If length(FUN.VALUE) == 1 a
vector of the same length as X is returned, otherwise
an array. If FUN.VALUE is not an array, the
result is a matrix with length(FUN.VALUE) rows and
length(X) columns, otherwise an array a with
dim(a) == c(dim(FUN.VALUE), length(X)).The (Dim)names of the array value are taken from the FUN.VALUE
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.
Note
sapply(*, simplify = FALSE, USE.NAMES = FALSE)
is
equivalent to lapply(*)
.
For historical reasons, the calls created by lapply
are
unevaluated, and code has been written (e.g., bquote
) that
relies on this. This means that the recorded call is always of the
form FUN(X[[i]], ...)
, with i
replaced by the current
(integer or double) index. This is not normally a problem, but it can
be if FUN
uses sys.call
or
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.\ifelse{latex}{\out{~}}{ } lapply(ll, function(x)
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’.
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
library(base)
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)
Community examples
# `simplify` behavior ```r set.seed(43770) x1 < replicate(10, sample(letters, 5, replace = TRUE), simplify = TRUE) x2 < replicate(10, sample(letters, 5, replace = TRUE), simplify = FALSE) print(x1) print(x2) y1 < sapply(1:10, function(i) sample(letters, i, replace = TRUE), simplify = TRUE) y2 < sapply(1:10, function(i) sample(letters, i, replace = TRUE), simplify = FALSE) print(y1) print(y2) ```
> mylist < list(c(3,8,1),c(5,4),c(3)) > lapply(mylist,rank)