[R] Regular expressions in R

[Joshua Wiley]

Hi Michael,

Your strings were long so I made a bit smaller example.  Sarah made
one good point, you want to be using gsub() not sub(), but when I use
your code, I do not think it even works precisely for one instance.
Try this on for size, you were 99% there:

## simplified cases
form1 <- c('product + action * mean + CTA + help + mean * product')
form2 <- c('product+action*mean+CTA+help+mean*product')

## what I believe your desired output is
'product + CTA + help'
'product+CTA+help'

gsub("\\s\\+\\s[[:alnum:]]*\\s\\*\\s[[:alnum:]]*", "", form1)
gsub("\\+[[:alnum:]]*\\*[[:alnum:]]*", "", form2)

## your code (using gsub() instead of sub())
gsub("\\+*\\s*[[:alnum:]]*\\s*\\*.[[:alnum:]]", "", form1)


######## Running on r57586 Windows x64 ########
> gsub("\\s\\+\\s[[:alnum:]]*\\s\\*\\s[[:alnum:]]*", "", form1)
[1] "product + CTA + help"
> gsub("\\+[[:alnum:]]*\\*[[:alnum:]]*", "", form2)
[1] "product+CTA+help"
>
> ## your code (using gsub() instead of sub())
> gsub("\\+*\\s*[[:alnum:]]*\\s*\\*.[[:alnum:]]", "", form1)
[1] "product ean + CTA + help roduct"

Hope this helps,

Josh

On Tue, Nov 15, 2011 at 9:18 AM, Michael Griffiths
<griffiths at upstreamsystems.com> wrote:
> Good afternoon list,
>
> I have the following character strings; one with spaces between the maths
> operators and variable names, and one without said spaces.
>
> form<-c('~ Sentence + LEGAL + Intro + Intro / Intro1 + Intro * LEGAL +
> benefit + benefit / benefit1 + product + action * mean + CTA + help + mean
> * product')
> form<-c('~Sentence+LEGAL+Intro+Intro/Intro1+Intro*LEGAL+benefit+benefit/benefit1+product+action*mean+CTA+help+mean*product')
>
> I would like to remove the following target strings, either:
>
> 1. '+ Intro * LEGAL' which is  '+ space name space * space name'
> 2. '+Intro*LEGAL' which is  '+ nospace name nospace * nospace name'
>
> Having delved into a variety of sites (e.g.
> http://www.zytrax.com/tech/web/regex.htm#search) investigating regular
> expressions I now have a basic grasp, but I am having difficulties removing
> ALL of the instances or 1. or 2.
>
> The code below removes just a SINGLE instance of the target string, but I
> was expecting it to remove all instances as I have \\*.[[allnum]]. I did
> try \\*.[[allnum]]*, but this did not work.
>
> form<-sub("\\+*\\s*[[:alnum:]]*\\s*\\*.[[:alnum:]]", "", form)
>
> I am obviously still not understanding something. If the list could offer
> some guidance I would be most grateful.
>
> Regards
>
> Mike Griffiths
>
>
>
> --
>
> *Michael Griffiths, Ph.D
> *Statistician
>
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-- 
Joshua Wiley
Ph.D. Student, Health Psychology
Programmer Analyst II, ATS Statistical Consulting Group
University of California, Los Angeles
https://joshuawiley.com/