From charles.dupont at vanderbilt.edu  Mon Apr 17 19:27:19 2006
From: charles.dupont at vanderbilt.edu (Charles Dupont)
Date: Mon, 17 Apr 2006 12:27:19 -0500
Subject: [Rd] (PR#8777) strsplit does [not] return correct value when
 spliting ""
In-Reply-To: <Pine.LNX.4.64.0604171534210.5712@gannet.stats.ox.ac.uk>
References: <20060417140025.3773A19B32@slim.kubism.ku.dk>
	<Pine.LNX.4.64.0604171534210.5712@gannet.stats.ox.ac.uk>
Message-ID: <4443CFF7.3040804@vanderbilt.edu>

Now using R 2.3.0.

I have a string that can be "".  I want to find the max screen width of 
the all the lines in the string. so I run the command

  > x <- c("hello", "bob is\ngreat", "foo", "", "bar")
  > substrings <- strsplit(x, "\n"), type="width")
  > sapply(substrings, FUN=function(x) max(nchar(x, type="width")))
which returns
[1]    5    6    3 -Inf    3

This happens because of the behavior of strsplit for a string that is not ""
  > strsplit("Hello\nBob", "\n")

it returns
[[1]]
[1] "Hello" "Bob"


for a string that is ""
  > strsplit("", "\n")

it returns
[[1]]
character(0)


I would expect
[[1]]
[1] ""

because "" is character vector of length 1 containing a string of length 
0, not a character vector of length 0.

For any other string if the split string is not matched in argument x 
then it returns the original string x.

The man page states in the value section that strsplit returns:
      A list of length 'length(x)' the 'i'-th element of which contains
      the vector of splits of 'x[i]'.

It mentions no change in behavior if the value of x[i] = "".

Prof Brian Ripley wrote:
> Please use a current version of R: we are at 2.3.0RC (and we do ask you 
> not to report on obselete versions).
> 
> What rule are you using, and where did you find it in the R documentation?
> 
> In fact
> 
>> strsplit("", " ")
> 
> [[1]]
> character(0)
> 
> which is not as you stated.   This is a feature, as it distinct from
> 
>> strsplit(" ", " ")
> 
> [[1]]
> [1] ""
> 
> Consider also
> 
>> strsplit("", "")
> 
> [[1]]
> character(0)
> 
>> strsplit("a", "")
> 
> [[1]]
> [1] "a"
> 
>> strsplit("ab", "")
> 
> [[1]]
> [1] "a" "b"
> 
> 
> On Mon, 17 Apr 2006, charles.dupont at vanderbilt.edu wrote:
> 
>> Full_Name: Charles Dupont
>> Version: 2.2.0
>> OS: linux
>> Submission from: (NULL) (160.129.129.136)
>>
>>
>> when
>>
>> strsplit("", " ")
>>
>> returns character(0)
>>
>> where as
>>
>> strsplit("a", " ")
>>
>> returns "a".
>>
>> these return values are not constiant with each other.
>>
>> Charles Dupont
>>
>> ______________________________________________
>> R-devel at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-devel
>>
>>
> 


-- 
Charles Dupont	Computer System Analyst		School of Medicine
		Department of Biostatistics	Vanderbilt University



[Rd] (PR#8777) strsplit does [not] return correct value when spliting ""
Charles Dupont