[Rd] paste(character(0), collapse="", recycle0=FALSE) should be ""

[Martin Maechler]

>>>>> suharto anggono--- via R-devel 
>>>>>     on Fri, 1 May 2020 03:05:37 +0000 (UTC) writes:

    > Without 'collapse', 'paste' pastes (concatenates) its arguments elementwise (separated by 'sep', " " by default). New in R devel and R patched, specifying recycle0 = FALSE makes mixing zero-length and nonzero-length arguments results in length zero. 

That's not intended.
(It's what should only happen with the new (non-default) recycle0=TRUE )

> The result of paste(n, "th", sep = "", recycle0 = FALSE) always have the same length as 'n'. Previously, the result is still as long as the longest argument, with the zero-length argument like "". If all og the arguments have length zero, 'recycle0' doesn't matter.

    > As far as I understand, 'paste' with 'collapse' as a character string is supposed to put together elements of a vector into a single character string. I think 'recycle0' shouldn't change it.

Well, not quite:  only  'recycle0=FALSE'  shouldn't change it
.. maybe this is what you meant anyway.

    > In current R devel and R patched, paste(character(0), collapse = "", recycle0 = FALSE) is character(0). I think it should be "", like paste(character(0), collapse="").

Definitely:  The intent of the new 'recycle0' argument is to 
provide a non-default possibility for paste(...., recycle0=TRUE) to behave more
like "arithmetic" functions where the recycling rules ensure that
if one argument has length 0 then the result has length 0:
i.e.,   paste(a,b,c,d,  recycle0=TRUE)      should recycle the same as
              a+b+c+d                       does recycle

Indeed, the default 'recycle0=FALSE'  should correspond to previous (R <= 4.0.0)
behavior entirely.

BUT from all I see, R-devel and R-patched's version of paste()
do behave as they should.  Also what you clim here is not true :

    > paste(c("4", "5"), "th", sep = "", collapse = ", ", recycle0 = FALSE)
    > is
    > "4th, 5th".
    > paste(c("4"     ), "th", sep = "", collapse = ", ", recycle0 = FALSE)
    > is
    > "4th".
    > I think
    > paste(c(        ), "th", sep = "", collapse = ", ", recycle0 = FALSE)
    > should be
    > "",
    > not character(0).

Rather, what I see is what the comments of the following code
lines claim (according to the intention of 'recycle0', contrary
some of your claims above) :


paste(character(0), collapse = "", recycle0 = FALSE) # is "", like
paste(character(0), collapse = "")
paste(character(0), collapse = "", recycle0 =  TRUE) # is character(0)

paste(c("4", "5"), "th", sep = "", collapse = ", ", recycle0 = FALSE) # is "4th, 5th"
paste(c("4"     ), "th", sep = "", collapse = ", ", recycle0 = FALSE) # is "4th"
paste(c(        ), "th", sep = "", collapse = ", ", recycle0 = FALSE) # is "th"
##
paste(c("4", "5"), "th", sep = "", collapse = ", ", recycle0 =  TRUE) # is "4th, 5th"
paste(c("4"     ), "th", sep = "", collapse = ", ", recycle0 =  TRUE) # is "4th"
paste(c(        ), "th", sep = "", collapse = ", ", recycle0 =  TRUE) # is character(0)


There must be a lapsus / misunderstanding somewhere.
I don't see any problem in the new behavior for now.

Best regards,
Martin