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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 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 pre-specified
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().
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 expression
object. Other objects (including classed objects) will be coerced
by base::as.list.
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.
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 if simplify = "array" the result may be an
array of “rank”
(length(dim(.))) one higher than the result
of FUN(X[[i]]).
logical; if TRUE and if X is character,
use X as names for 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 lapply().
logical; if true, simplify2array() will produce a
(“higher rank”) array when appropriate, whereas
higher = FALSE would return a matrix (or vector) only.
These two cases correspond to sapply(*, simplify = "array") or
simplify = TRUE, respectively.
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.
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.
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 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.
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.
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.
# NOT RUN {
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)
# }
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