string - counting specific words across multiple columns in R

Question

I have a data frame like this

df <- data.frame(id=c(1, 2, 3, 4, 5), staple_1=c("potato", "cassava","rice","fruit","coffee"), staple_2=c("cassava","beer","peanuts","rice","yams"), staple_3=c("rice","peanuts","fruit","fruit","rice"))

I also have a character vector like this

staples<-c("potato","cassava","rice","yams")

I would like to create a new variable that is the row sum of the occurrence of any of the words in the "staples" character vector. The outcome of which should look like this

df$staples<-c(3,1,1,1,2)

I have tried several approaches and nothing has worked so far. My actual dataframe is much bigger and character vector has 20 or more words in it. I'm sure there is a simple solution but that I am missing it somehow.

Answer 1

A simple apply will do it.

apply(df, 1, function(x) sum(staples %in% x))
#[1] 3 1 1 1 2

df$staples <- apply(df, 1, function(x) sum(staples %in% x))