Count subset of words occurrences in R?

In R, suppose I have a list of strings like the following:

str_list <- list("corn is food", "corn is good")

If I want to count the number of times each word in some subset of words like "corn" and "food" occur in each element, is there any way to do this? For example, based on str_list, I would want a vector [2, 1] that counted food (1x) and corn (1x) in the first element, and corn (1x) in the second element. I do NOT want to count just a single word like "corn", which can just be done with the stringr::str_count() function).

You could solve your problem as follow:

colSums(sapply(words, stringi::stri_count_fixed, str=str_list))
# corn food 
#    2    1

# or 
stringi::stri_count_fixed(paste0(str_list, collapse=" "), words)
# [1] 2 1

data

str_list <- list("corn is food", "corn is good")
words <- c("corn", "food")

With base R, You can use sapply + grep + lengths:

lengths(sapply(words, grep, str_list))

# corn food 
#    2    1

Update

As @Onyambu points out, if a word is repeated in a sentence, grep will not capture the repeat. A revision is made by replacing grep() with gregexpr().

sapply(words, \(x) sum(gregexpr(x, toString(str_list))[[1]] > 0))

An equivalent solution with stringr::str_count():

colSums(sapply(words, stringr::str_count, string = str_list))

Data

str_list <- list("corn is food", "corn is good")
words <- c("corn", "food")

If I understood properly what you need, the code below should solve it, although we do have str_count in there:

library(stringr)

str_list <- list("corn is food", "corn is good")
word_list <- c("corn", "food")

count_words <- function(string, words) {
  sum(sapply(words, function(word) str_count(string, word)))
}

result <- sapply(str_list, count_words, word_list)

which outputs the required vector:

> print(result)
[1] 2 1

You can try strsplit + table like below

> table(unlist(strsplit(unlist(str_list), "\\W+")))[word_list]

corn food
   2    1