Help with text separation

Thank you Sarah,

Your reply was very helpful. I have the added difficulty that I am not 

dealing with single A-Z characters, but quite often have the following
situation:

form<-c('~Sentence+LEGAL+Intro+Intro/Intro1+Intro*LEGAL+benefit+benefit/
benefit1+product+action+mean+CTA*help')

and again, I need to remove the +'CTA*help' part of the character 

However, in another instance I may have

form<-c('~Sentence*LEGAL+Intro+Intro/Intro1+Intro*LEGAL+benefit+benefit/
benefit1+product+action+mean+CTA*help')


In this case I would need to remove 'Sentence*LEGAL+' from form.


Can this be accomplished in the same manner?

Many thanks, once again, for your help

Mike Griffiths



On Mon, Nov 14, 2011 at 12:09 PM, Sarah Goslee 

Hi,

On Mon, Nov 14, 2011 at 4:20 AM, Michael Griffiths
<griffiths at upstreamsystems.com> wrote:

Good morning R list,

My apologies if this has *already* answered elsewhere, but I have 

found

the answer that I am looking for.

I have a character string, i.e.


form<-c('~ A + B + C + C / D + E + E / F + G + H + I + J + K + L * 

Now, my aim is to find the position of all those instances of '*' 

remove said '*'. However, I would also like to remove the preceding
variable name before the '*', the math operator preceding this, and 

the variable name after the '*'. So, here I would like to remove 

You just want to get rid of them? gsub() it is.

I've changed your formula a little bit to better demonstrate what's 

on:

form<-c('~ A + B * C + C / D + E + E / F * G + H + I + J + K + L * 

gsub(" \\+ [A-Z] \\* [A-Z]", "", form)

[1] "~ A + C / D + E + E / F * G + H + I + J + K"

That regular expression will take out a
space
+
any capital letter
space
*
space
any capital letter.

It will take out all occurrences of that sequence, but won't take out
occurrences of * not in that sequence.

If you don't want the spaces, you don't need them. Just take them out
of the regular expression as well.

Not that strsplit() was remotely the right tool here, but you can
split into characters without a separator:

form <- 'abcd'
strsplit(form, '')

[[1]]
[1] "a" "b" "c" "d"

Sarah

So, far I have come up with the following code:

parts<-strsplit(form,' ')
index<-which(unlist(parts)=="*")
for (i in 1:length(index)){
   parts[[1]][index[i]]<-list(NULL)
   parts[[1]][index[i]+1]<-list(NULL)
   parts[[1]][index[i]-1]<-list(NULL)
   parts[[1]][index[i]-2]<-list(NULL)
}
new.form<-unlist(parts)

form<-new.form[0]
for (i in 1: length(new.form)){
   form<-paste(form,new.form[i], sep="")
}

However, as you can see, I have had to use strsplit in, what I 

rather clumsy manner, as the character string (form) has to be in a

certain

format. All variables and maths operators require a space between 

order for strsplit to work in the manner I require.

I would very much like to accomplish what the above code already 

but

without the need for the initial character string having the need 

aforementioned spaces.

If the list can offer help, I would be most appreciative.

Yours

Mike Griffiths

--
Sarah Goslee
http://www.functionaldiversity.org

-- 

*Michael Griffiths, Ph.D
*Statistician

*Upstream Systems*

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