Check for a list of strings (words) in a text (phrase)

Question

Is there an elegant way, other than looping, to test if a word which belong to a list is found in a phrase? I'm thinking something like list comprehension of one of the apply functions. Ex:

words <- c("word1", "word2", "word3")
text <- "This is a text made off of word1 and possibly word2 and so on."

The output should return TRUE if any of the words is founded in text and which word is founded.

Answer 1

grepl to the rescue.

sapply(words, grepl, text)

# word1 word2 word3 
#  TRUE  TRUE FALSE

This considers each element of words, in turn, and returns a logical (TRUE if the the word appears in text, and FALSE if not).

If you want to ensure that the exact words are sought, then you can use:

sapply(words, function(x) grepl(sprintf('\\b%s\\b', x), text))

This will prevent word1 from returning TRUE when text has sword123 but lacks word1. It might make less sense though if words has multi-word elements.

Answer 2

Look at the package stringr. I think the function you need to use is str_detect or str_locate_all. It's is to include this function in sapply.

library(stringr)

str_detect(text, words)

str_locate_all(text, words)