R: How to delete words other than specific words in a corpus

Question

In the corpus "tkn_pb" , I would like to delete all words except for some keywords I chose (ex. "attack" and "gunman"). Is it possicle to do this?

Answer 1

You can use whichand grepl to subset your corpus:

Data:

sample_tokens <- c("word", "another","a", "new", "word token", "one", "more", "and", "another one")

Remove all words except "a" and "and":

sample_tokens[which(grepl("\\b(a|and)\\b", sample_tokens))]
[1] "a"   "and"

EDIT:

If the corpus is a list, then this solution suggested by @John would work:

Data:

sample_tokens <- list(c("word", "another","a", "new", "word token", "one", "more", "and", "another one"),
               c("yet", "a", "few", "more", "words"),
               c("and", "so on"))

lapply(sample_tokens, function(x) x[which(grepl("\\b(a|and)\\b", x))])
[[1]]
[1] "a"   "and"

[[2]]
[1] "a"

[[3]]
[1] "and"