Add 'simplify' argument to Reduce() (PR#18569, from Steve Martin).

git-svn-id: https://svn.r-project.org/R/trunk@84737 00db46b3-68df-0310-9c12-caf00c1e9a41

src/library/base/R/funprog.R

@@ -17,7 +17,7 @@
 # https://www.R-project.org/Licenses/
 
 Reduce <-
-function(f, x, init, right = FALSE, accumulate = FALSE)
+function(f, x, init, right = FALSE, accumulate = FALSE, simplify = TRUE)
 {
  mis <- missing(init)
  len <- length(x)
@@ -95,7 +95,7 @@ function(f, x, init, right = FALSE, accumulate = FALSE)
  ## If all results have length one, we can simplify.
  ## (Note that we do not simplify to arrays in case all results
  ## have a common length > 1.)
- if(all(lengths(out) == 1L))
+ if(all(lengths(out) == 1L) && simplify)
  out <- unlist(out, recursive = FALSE)
  out
  }

src/library/base/man/funprog.Rd

@@ -1,6 +1,6 @@
 % File src/library/base/man/funprog.Rd
 % Part of the R package, https://www.R-project.org
-% Copyright 1995-2021 R Core Team
+% Copyright 1995-2023 R Core Team
 % Distributed under GPL 2 or later
 \name{funprog}
 \alias{Filter}
@@ -23,7 +23,7 @@
  }
 }
 \usage{
-Reduce(f, x, init, right = FALSE, accumulate = FALSE)
+Reduce(f, x, init, right = FALSE, accumulate = FALSE, simplify = TRUE)
 Filter(f, x)
 Find(f, x, right = FALSE, nomatch = NULL)
 Map(f, ...)
@@ -44,6 +44,9 @@ Position(f, x, right = FALSE, nomatch = NA_integer_)
  \item{accumulate}{a logical indicating whether the successive reduce
  combinations should be accumulated. By default, only the final
  combination is used.}
+ \item{simplify}{a logical indicating whether accumulated results
+ should be simplified (by unlisting) in case they all are length
+ one.}
  \item{nomatch}{the value to be returned in the case when
  \dQuote{no match} (no element satisfying the predicate) is found.}
  \item{\dots}{vectors to which the function is \code{Map()}ped, and other