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
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
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 use.
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 possible? For
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 (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 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
... 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
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
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
as.list in 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 = 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
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
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
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
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.
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[[0L]], ...), with
0L replaced by the current integer index. This is not normally a problem, but it can be if
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.
lapply(ll, function(x) is.numeric(x)) is required in R 2.7.1 to ensure that method dispatch for
is.numeric occurs correctly.
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’.
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)
Documentation reproduced from R 2.15.3. License: GPL-2.