R help - Nov 2003 - Q. About String indexing

Hi all - this is a very basic question: how does one index substrings of a
character string, for example get the 2nd through 5th characters of the string
"testing", in the R language? Indexing with square brackets seems only
to work for vectors, lists, etc., and although I've found plenty of
functions for concatenating strings, running substitutions with regexps and the
like, I seem to be at a loss when it comes to indexing or selecting substrings.

I'm sure I'm missing something very obvious here, but I ask only after
having scoured the basic help manuals.

I am not so subscribed to this list, so if any replies could be sent directly to
me.

Thanks very much,
-----Ben
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On Thu, 2003-11-06 at 19:53, Ben Day wrote:
> Hi all - this is a very basic question: how does one index substrings
> of a character string, for example get the 2nd through 5th characters
> of the string "testing", in the R language? Indexing with square
> brackets seems only to work for vectors, lists, etc., and although
> I've found plenty of functions for concatenating strings, running
> substitutions with regexps and the like, I seem to be at a loss when
> it comes to indexing or selecting substrings.
> 
> I'm sure I'm missing something very obvious here, but I ask only
after
> having scoured the basic help manuals.
> 
> I am not so subscribed to this list, so if any replies could be sent
> directly to me.
> 
> Thanks very much,
> -----Ben

unlist(strsplit("testing",""))[2:5]
[1] "e" "s" "t" "i"

Use strsplit() to convert the string into a list of characters, where
""
is the separator.

Then use unlist() to convert the list into a vector and index the 2:5
characters.

See ?strsplit and ?unlist

HTH,

Marc Schwartz

Dear Ben and Mark,

substring and substr are also helpful here.

John

At 08:10 PM 11/6/2003 -0600, Marc Schwartz wrote:
>On Thu, 2003-11-06 at 19:53, Ben Day wrote:
> > Hi all - this is a very basic question: how does one index substrings
> > of a character string, for example get the 2nd through 5th characters
> > of the string "testing", in the R language? Indexing with
square
> > brackets seems only to work for vectors, lists, etc., and although
> > I've found plenty of functions for concatenating strings, running
> > substitutions with regexps and the like, I seem to be at a loss when
> > it comes to indexing or selecting substrings.
> >
> > I'm sure I'm missing something very obvious here, but I ask
only after
> > having scoured the basic help manuals.
> >
> > I am not so subscribed to this list, so if any replies could be sent
> > directly to me.
> >
> > Thanks very much,
> > -----Ben
>
>
>unlist(strsplit("testing",""))[2:5]
>[1] "e" "s" "t" "i"
>
>Use strsplit() to convert the string into a list of characters, where
""
>is the separator.
>
>Then use unlist() to convert the list into a vector and index the 2:5
>characters.
>
>See ?strsplit and ?unlist
>
>HTH,
>
>Marc Schwartz
>
>______________________________________________
>R-help at stat.math.ethz.ch mailing list
>https://www.stat.math.ethz.ch/mailman/listinfo/r-help
-----------------------------------------------------
John Fox
Department of Sociology
McMaster University
Hamilton, Ontario, Canada L8S 4M4
email: jfox at mcmaster.ca
phone: 905-525-9140x23604
web: www.socsci.mcmaster.ca/jfox

On Thu, 2003-11-06 at 20:24, John Fox wrote:
> Dear Ben and Mark,
> 
> substring and substr are also helpful here.
> 
> John

Quite true. 

As usual, there is usually more than one way to do things. The above
approach, given the C code, would be faster as the source vector and the
offsets of the substring increase in size.

This would become more influential if you want the resultant characters
as a single substring as opposed to a vector of the characters, which my
initial solution would yield.
> unlist(strsplit("testing", ""))[2:5]
[1] "e" "s" "t" "i"
> substr("testing", 2, 5)
[1] "esti"

Thanks John.

Marc