R devel - Jun 2010 - Argument recycling in substring()

Hi,

According to its man page substring() "expands (its) arguments
cyclically to the length of the longest _provided_ none are of
zero length".

So, as expected, I get an error here:

   > substring("abcd", first=2L, last=integer(0))
   Error in substring("abcd", first = 2L, last = integer(0)) :
     invalid substring argument(s)

But I don't get one here:

   > substring(character(0), first=1:2, last=3L)
   character(0)

which is unexpected.

Otherwise, yes substring() will recycle its arguments to the
length of the longest:

   > substring("abcd", first=1:3, last=4:3)
   [1] "abcd" "bc"   "cd"

Cheers,
H.

-- 
Herv? Pag?s

Program in Computational Biology
Division of Public Health Sciences
Fred Hutchinson Cancer Research Center
1100 Fairview Ave. N, M2-B876
P.O. Box 19024
Seattle, WA 98109-1024

E-mail: hpages at fhcrc.org
Phone:  (206) 667-5791
Fax:    (206) 667-1319

>>>>> "HP" == Herv? Pag?s <hpages at fhcrc.org>
>>>>>     on Thu, 03 Jun 2010 17:53:33 -0700 writes:
    HP> Hi,
    HP> According to its man page substring() "expands (its) arguments
    HP> cyclically to the length of the longest _provided_ none are of
    HP> zero length".

    HP> So, as expected, I get an error here:

    >> substring("abcd", first=2L, last=integer(0))
    HP> Error in substring("abcd", first = 2L, last = integer(0)) :
    HP> invalid substring argument(s)

    HP> But I don't get one here:

    >> substring(character(0), first=1:2, last=3L)
    HP> character(0)

    HP> which is unexpected.
according to the docu.

My gut feeling would say that the documentation should be
updated in this case, rather than the implementation.

RFC! other opinions?


    HP> Otherwise, yes substring() will recycle its arguments to the
    HP> length of the longest:

    >> substring("abcd", first=1:3, last=4:3)
    HP> [1] "abcd" "bc"   "cd"




    HP> Cheers,
    HP> H.

    HP> -- 
    HP> Herv? Pag?s

    HP> Program in Computational Biology
    HP> Division of Public Health Sciences
    HP> Fred Hutchinson Cancer Research Center
    HP> 1100 Fairview Ave. N, M2-B876
    HP> P.O. Box 19024
    HP> Seattle, WA 98109-1024

    HP> E-mail: hpages at fhcrc.org
    HP> Phone:  (206) 667-5791
    HP> Fax:    (206) 667-1319

    HP> ______________________________________________
    HP> R-devel at r-project.org mailing list
    HP> https://stat.ethz.ch/mailman/listinfo/r-devel

> According to its man page substring() "expands (its) arguments
> cyclically to the length of the longest _provided_ none are of
> zero length".
>
> So, as expected, I get an error here:
>
> ?> substring("abcd", first=2L, last=integer(0))
> ?Error in substring("abcd", first = 2L, last = integer(0)) :
> ? ?invalid substring argument(s)
>
> But I don't get one here:
>
> ?> substring(character(0), first=1:2, last=3L)
> ?character(0)
>
> which is unexpected.
If you want a set of string functions that strive to be simple and
consistent you might want to look at the stringr package.  And since
it's a new package, I'm very keen to remove any inconsistencies.

Hadley

-- 
Assistant Professor / Dobelman Family Junior Chair
Department of Statistics / Rice University
http://had.co.nz/