[Rd] Wish: keep names in mapply() result

[Gregor Gorjanc]

Hello!

I have noticed that mapply() drops names in R 2.3.1 as well as in
r-devel. Here is a simple example:

l <- list(a=1, b=2)
k <- list(1)
mapply(FUN="+", l, k)
[1] 2 3
mapply(FUN="+", l, k, SIMPLIFY=FALSE)
[[1]]
[1] 2

[[2]]
[1] 3

Help page does not indicate that this should happen. Argument USE.NAMES
does not have any effect here as it used only in a bit special
situation: "If the first ... argument is character and the result does
not already have names, use it as the names." But result is always
without names as shown above. Did I miss any peculiarities?

This is not consistent with lapply, which keeps names i.e.

lapply(l, "+", 1)
$a
[1] 2

$b
[1] 3

I have attached and copied (at the end) patch proposal against SVN that
adds names back to the result if x had it (only R as my C is ...). This
way it would also be consistent with lapply. make check-all seems to be
happy with changes. Now we get:

mapply(FUN="+", l, k)
a b
2 3

mapply(FUN="+", l, k, SIMPLIFY=FALSE)
$a
[1] 2

$b
[1] 3

And if we had "character" (with some variations) for first ... then:

l <- list(a="1", b="2")
mapply(FUN="paste", l, k)
    a     b
"1 1" "2 1"

l <- list("1", "2")
mapply(FUN="paste", l, k)
[1] "1 1" "2 1"

l <- c("1", "2")
mapply(FUN="paste", l, k)
    1     2
"1 1" "2 1"

Index: src/library/base/R/mapply.R
===================================================================
--- src/library/base/R/mapply.R (revision 39024)
+++ src/library/base/R/mapply.R (working copy)
@@ -3,8 +3,16 @@
     FUN <- match.fun(FUN)
     dots <- list(...)

+    if(!is.null(names(dots[[1]]))) {
+        isNamed <- TRUE
+        namesX <- names(dots[[1]])
+    } else {
+        isNamed <- FALSE
+    }
+
     answer<-.Call("do_mapply", FUN, dots, MoreArgs, environment(),
                   PACKAGE="base")
+    if(isNamed) names(answer) <- namesX

     if (USE.NAMES && length(dots) && is.character(dots[[1]]) &&
         is.null(names(answer))) names(answer) <- dots[[1]]
@@ -47,4 +55,4 @@
     }
     formals(FUNV) <- formals(FUN)
     FUNV
-}
\ No newline at end of file
+}

-- 
Lep pozdrav / With regards,
    Gregor Gorjanc

----------------------------------------------------------------------
University of Ljubljana     PhD student
Biotechnical Faculty
Zootechnical Department     URI: http://www.bfro.uni-lj.si/MR/ggorjan
Groblje 3                   mail: gregor.gorjanc <at> bfro.uni-lj.si

SI-1230 Domzale             tel: +386 (0)1 72 17 861
Slovenia, Europe            fax: +386 (0)1 72 17 888

----------------------------------------------------------------------
"One must learn by doing the thing; for though you think you know it,
 you have no certainty until you try." Sophocles ~ 450 B.C.
----------------------------------------------------------------------
-------------- next part --------------
An embedded and charset-unspecified text was scrubbed...
Name: mapply.R.namesPatch
Url: https://stat.ethz.ch/pipermail/r-devel/attachments/20060831/0a234e2c/attachment-0004.ksh