removeWords.r

library(tm)

x <- paste(sample(c(LETTERS, " "), 1e4, rep = T), collapse = "")
words <- stopwords("english")
match <- sprintf("\\b(%s)\\b", paste(words, collapse = "|"))

system.time(gsub(match, "", x))
# Takes ~0.08 s

# Home made solution, not quite equivalent but close.
system.time({
  xs <- strsplit(x, " ", fixed = TRUE)[[1]]
  d <- vapply(words, grepl, x = xs, fixed = TRUE, 
    FUN.VALUE = logical(length(xs)))
  paste(x[rowSums(d) == 0], collapse = " ")
})
# Takes ~0.04 s

# But the perl regexp engine is way faster than either
system.time(gsub(match, "", x, perl = TRUE))
# Takes ~0.01 s