r - Difference of two character vectors with substring

Question

I have two lists:

a <- c("da", "ba", "cs", "dd", "ek")
b <- c("zyc", "ulk", "mae", "csh", "ddi", "dada")

I want to remove the elements from list b which would have a substring match with any of the values in a, e.g.

grepl("da","dada") # TRUE

How would you go about doing this efficiently?

Answer 1

We can paste the 'a' elements to a single string with | as the delimiter, use that as pattern in grepl, negate (!) to subset 'b'.

 b[!grepl(paste(a, collapse="|"), b)]