| lapply {base} | R Documentation |
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).
lapply(X, FUN, ...) sapply(X, FUN, ..., simplify = TRUE, USE.NAMES = TRUE) replicate(n, expr, simplify = TRUE)
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. |
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.
Users of S4 classes should pass a list to lapply: the internal
coercion is done by the system as.list in the base namespace
and not one defined by a user (e.g. by setting S4 methods on the
system function).
For lapply and sapply(simplify=FALSE), a list.
For sapply(simplify=TRUE) and replicate: 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 < real < complex < character
< list < expression, after coercion of pairlists tolists.
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[[0L]], ...), with 0L replaced by the current
integer index. This 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. lapply(ll, function(x) is.numeric(x)) is required in
R 2.7.1 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.
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.
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) 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)