[R] regular expression help to extract specific strings from text

[Gabor Grothendieck]

strapply in gsubfn can extract matches based on content which seems to
be what you want:

library(gsubfn)

f <- function(...) sapply(list(...), paste, collapse = ", ")

DF <- data.frame(x,
	Source = strapply(x, "^(\\w+):", c, simplify = f),
	Mentions = strapply(x, "@(\\w+)", c, simplify = f),
	HashTags = strapply(x, "#(\\w+)", c, simplify = f))

DF[DF == ""] <- NA



On Wed, Mar 31, 2010 at 9:20 AM, Tony B <tony.breyal at googlemail.com> wrote:
> Dear all,
>
> Lets say I have the following:
>
>> x <- c("Eve: Going to try something new today...", "Adam: Hey @Eve, how are you finding R? #rstats", "Eve: @Adam, It's awesome, so much better at statistics that #Excel ever was! @Cain & @Able disagree though :(", "Adam: @Eve I'm sure they'll sort it out :)", "blahblah")
>> x
> [1] "Eve: Going to try something new
> today..."
> [2] "Adam: Hey @Eve, how are you finding R?
> #rstats"
> [3] "Eve: @Adam, It's awesome, so much better at statistics that
> \n#Excel ever was! @Cain & @Able disagree though :("
> [4] "Adam: @Eve I'm sure they'll sort it
> out :)"
> [5] "blahblah"
>
> I would like to come up with a data frame which looks like this
> (pulling out the usernames and #tags):
>
>> data.frame(Msg = x, Source = c("Eve", "Adam", "Eve", "Adam", NA), Mentions = c(NA, "Eve", "Adam, Cain, Able", "Eve", NA), HashTags = c(NA, "rstats", "Excel", NA, NA))
>
> The best I can do so far is:
>
> source <- lapply(x, function (x) {
>   tmp <- strsplit(x, ":", fixed = TRUE)
>   if(length(tmp[[1]]) < 2) {
>     tmp <- c(NA, tmp)
>   }
>   return(tmp[[1]][1])
>  } )
> source <- unlist(source)
>
> [1] "Eve"  "Adam" "Eve"  "Adam" NA
>
> I can't work out how to extract the usernames starting with '@' or the
> #tags. I can identify them using gsub and replace them, but I don't
> know how to just extract those terms only, e.g. sort of the opposite
> of the following
>
>> gsub("@([A-Za-z0-9_]+)", "@[...]", x)
> [1] "Eve: Going to try something new today..."
> [2] "Adam: Hey @[...], how are you finding R? #rstats"
> [3] "Eve: @[...], It's awesome, so much better at statistics that
> #Excel ever was! @[...] & @[...] disagree though :("
> [4] "Adam: @[...] I'm sure they'll sort it out :)"
> [5] "blahblah"
>
> and
>
>> gsub("#([A-Za-z0-9_]+)", "#[...]", x)
> [1] "Eve: Going to try something new today..."
> [2] "Adam: Hey @Eve, how are you finding R? #[...]"
> [3] "Eve: @Adam, It's awesome, so much better at statistics that
> #[...] ever was! @Cain & @Able disagree though :("
> [4] "Adam: @Eve I'm sure they'll sort it out :)"
> [5] "blahblah"
>
> I hope that makes sense, and thank you kindly in advance for your
> time.
> Tony Breyal
>
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