[R] subbing a string vector for another string vector

[David Winsemius]

On Sep 8, 2010, at 4:45 PM, jlemaitre wrote:

>
> I have a data frame with two columns:
>       url.img                               patt.url
> 1    http://$IMAGE_ID$            www.url.com/image.jpg
> 2    $IMAGE_ID$                      http://www.blah.com/image.gif
> ...
>
> I want to replace "$IMAGE_ID$" with the corresponding entry in the  
> pattern
> column such that the result would appear as follows:

A) Drop the use of the name "pattern" because it is the argument name  
for regex functions. Name it something else like "patt.url".  
Furthermore "image" is also a function name so use somehting more  
specific there too, say "url.img"

B) use grep(<grep-pattern>, df$url.img) to identify the rows of  
"patt.url" you want to assemble.

Perhaps:

df[ grep("\\$IMAGE\\_ID\\$", df$url.img), "patt.url"]


>
> url
> http://www.url.com/image.jpg
> http://www.blah.com/image.gif
>
> Using something like  > gsub(,image,pattern) doesn't work
> because it only takes uses the first entry in "pattern" as the  
> replacement
> for all "image" entries:
>
> url
> http://www.url.com/image.jpg
> www.url.com/image.jpg
>
> Please help.
> Thanks.
>
>
>
>
> -- 
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David Winsemius, MD
West Hartford, CT