regex - How to escape a question mark in R?

Question

I am trying to grep a vector of strings and some of them contain question marks.

I am doing:

grep('?',vectorofStrings) and getting this error:

Error: '?' is an unrecognized escape in character string starting "?"

How can I determine the proper escaping procedure for '?'

Answer 1

You have to escape as well:

vectorOfStrings <- c("Where is Waldo?", "I don't know", "This is ? random ?")
grep("\?", vectorOfStrings)
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[1] 1 3