[R] extracting every nth character from a string...

[David L Carlson]

No rex, but not much less complicated, than your original but a different approach:

> i <- seq(1, nchar(str), 2)
> paste0(mapply(substr, str, i, i), collapse="")
[1] "ACEG"

-------------------------------------
David L Carlson
Department of Anthropology
Texas A&M University
College Station, TX 77840-4352

-----Original Message-----
From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of Gabor Grothendieck
Sent: Sunday, September 6, 2015 10:27 AM
To: Evan Cooch
Cc: r-help at r-project.org
Subject: Re: [R] extracting every nth character from a string...

This uses a regular expression but is shorter:

> gsub("(.).", "\\1", "ABCDEFG")
[1] "ACEG"

It replaces each successive pair of characters with the first of that
pair.  If there is an odd number of characters then the last character is
not matched and therefore kept -- thus it works properly for both even and
odd.


On Sat, Sep 5, 2015 at 4:59 PM, Evan Cooch <evan.cooch at gmail.com> wrote:

> Suppose I had the following string, which has length of integer multiple
> of some value n. So, say n=2, and the example string has a length of  (2x4)
> = 8 characters.
>
> str <- "ABCDEFGH"
>
> What I'm trying to figure out is a simple, base-R coded way (which I
> heuristically call StrSubset in the following) to extract every nth
> character from the string, to generate a new string.
>
> So
>
> str <- "ABCDEFGH"
>
> new_str <- StrSubset(str);
>
> print(new_str)
>
> which would yield
>
> "ACEG"
>
>
> Best I could come up with is something like the following, where I extract
> every odd character from the string:
>
> StrSubset <- function(string)
>       {
> paste(unlist(strsplit(string,""))[seq(1,nchar(string),2)],collapse="") }
>
>
> Anything more elegant come to mind? Trying to avoid regex if possible
> (harder to explain to end-users), but if that meets the 'more elegant'
> sniff test, happy to consider...
>
> Thanks in advance...
>
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>



-- 
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