grep using a character vector with multiple patterns

Question

I am trying to use grep to test whether a vector of strings are present in an another vector or not, and to output the values that are present (the matching pat

Answer 1

This should work:

grep(pattern = 'A1|A9|A6', x = myfile$Letter)

Or even more simply:

library(data.table)
myfile$Letter %like% 'A1|A9|A6'