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% File src/library/base/man/rapply.Rd
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% File src/library/base/man/rapply.Rd
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% Part of the R package, https://www.R-project.org
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% Part of the R package, https://www.R-project.org
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% Copyright 1995-2007 R Core Team
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% Copyright 1995-2018 R Core Team
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% Distributed under GPL 2 or later
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% Distributed under GPL 2 or later
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\name{rapply}
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\name{rapply}
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\alias{rapply}
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\alias{rapply}
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\title{Recursively Apply a Function to a List}
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\title{Recursively Apply a Function to a List}
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\description{
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\description{
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\code{rapply} is a recursive version of \code{\link{lapply}}.
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\code{rapply} is a recursive version of \code{\link{lapply}} with
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flexibility in \emph{how} the result is structured (\code{how = ".."}).
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}
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}
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\usage{
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\usage{
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rapply(object, f, classes = "ANY", deflt = NULL,
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rapply(object, f, classes = "ANY", deflt = NULL,
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how = c("unlist", "replace", "list"), ...)
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how = c("unlist", "replace", "list"), ...)
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}
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}
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\arguments{
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\arguments{
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\item{object}{A list.}
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\item{object}{a \code{\link{list}} or \code{\link{expression}}, i.e., \dQuote{list-like}.}
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\item{f}{A function of a single argument.}
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\item{f}{a \code{\link{function}} of one \dQuote{principal} argument,
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passing further arguments via \code{\dots}.}
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\item{classes}{A character vector of \code{\link{class}} names, or
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\item{classes}{character vector of \code{\link{class}} names, or
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\code{"ANY"} to match any class.}
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\code{"ANY"} to match any class.}
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\item{deflt}{The default result (not used if \code{how = "replace"}).}
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\item{deflt}{The default result (not used if \code{how = "replace"}).}
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\item{how}{A character string partially matching the three possibilities given:
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\item{how}{character string partially matching the three possibilities given:
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see \sQuote{Details}.}
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see \sQuote{Details}.}
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\item{\dots}{additional arguments passed to the call to \code{f}.}
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\item{\dots}{additional arguments passed to the call to \code{f}.}
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}
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}
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\details{
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\details{
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This function has two basic modes. If \code{how = "replace"}, each
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This function has two basic modes. If \code{how = "replace"}, each
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element of the list which is not itself a list and has a class
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element of \code{object} which is not itself list-like and has a class
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included in \code{classes} is replaced by the result of applying
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included in \code{classes} is replaced by the result of applying
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\code{f} to the element.
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\code{f} to the element.
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If the mode is \code{how = "list"} or \code{how = "unlist"}, the list
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Otherwise, with mode \code{how = "list"} or \code{how = "unlist"},
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conceptually \code{object}
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is copied, all non-list elements which have a class included in
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is copied, all non-list elements which have a class included in
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\code{classes} are replaced by the result of applying \code{f} to the
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\code{classes} are replaced by the result of applying \code{f} to the
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element and all others are replaced by \code{deflt}. Finally, if
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element and all others are replaced by \code{deflt}. Finally, if
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\code{how = "unlist"}, \code{unlist(recursive = TRUE)} is called on
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\code{how = "unlist"}, \code{unlist(recursive = TRUE)} is called on
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the result.
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the result.
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The semantics differ in detail from \code{\link{lapply}}: in
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The semantics differ in detail from \code{\link{lapply}}: in
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particular the arguments are evaluated before calling the C code.
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particular the arguments are evaluated before calling the C code.
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In \R 3.5.x and earlier, \code{object} was required to be a list,
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which was \emph{not} the case for its list-like components.
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}
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}
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\value{
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\value{
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If \code{how = "unlist"}, a vector, otherwise a list of similar
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If \code{how = "unlist"}, a vector, otherwise \dQuote{list-like}
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structure to \code{object}.
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of similar structure as \code{object}.
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}
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}
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\seealso{
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\seealso{
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\code{\link{lapply}}, \code{\link{dendrapply}}.
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\code{\link{lapply}}, \code{\link{dendrapply}}.
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}
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}
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\references{
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\references{
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\emph{Programming with Data}.
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\emph{Programming with Data}.
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Springer.\cr
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Springer.\cr
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(\code{rapply} is only described briefly there.)
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(\code{rapply} is only described briefly there.)
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}
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}
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\examples{
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\examples{
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X <- list(list(a = pi, b = list(c = 1:1)), d = "a test")
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X <- list(list(a = pi, b = list(c = 1L)), d = "a test")
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# the "identity operation":
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rapply(X, function(x) x, how = "replace")
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rapply(X, function(x) x, how = "replace") -> X.; stopifnot(identical(X, X.))
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rapply(X, sqrt, classes = "numeric", how = "replace")
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rapply(X, sqrt, classes = "numeric", how = "replace")
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rapply(X, nchar, classes = "character",
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rapply(X, deparse, control = "all") # passing extras. argument of deparse()
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deflt = as.integer(NA), how = "list")
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rapply(X, nchar, classes = "character",
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rapply(X, nchar, classes = "character", deflt = NA_integer_, how = "list")
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deflt = as.integer(NA), how = "unlist")
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rapply(X, nchar, classes = "character", deflt = NA_integer_, how = "unlist")
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rapply(X, nchar, classes = "character", how = "unlist")
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rapply(X, nchar, classes = "character", how = "unlist")
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rapply(X, log, classes = "numeric", how = "replace", base = 2)
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rapply(X, log, classes = "numeric", how = "replace", base = 2)
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## with expression() / list():
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E <- expression(list(a = pi, b = expression(c = C1 * C2)), d = "a test")
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LE <- list(expression(a = pi, b = expression(c = C1 * C2)), d = "a test")
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rapply(E, nchar, how="replace") # "expression(c = C1 * C2)" are 23 chars
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rapply(E, nchar, classes = "character", deflt = NA_integer_, how = "unlist")
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rapply(LE, as.character) # a "pi" | b1 "expression" | b2 "C1 * C2" ..
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rapply(LE, nchar) # (see above)
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stopifnot(exprs = {
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identical(E , rapply(E , identity, how = "replace"))
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identical(LE, rapply(LE, identity, how = "replace"))
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})
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}
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}
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\keyword{iteration}
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\keyword{iteration}
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\keyword{list}
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\keyword{list}
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