Finding all elements of a string vector that end with a given string in R

Question

Suppose I have a character vector:

test <- c("a##", "b", "c##", "d", "e")

I want to retrieve the indexes of elements ending with "##".

How can I do that?

Answer 1

Here is one method using grep:

grep("##$", test)

This returns indices 1 and 3 as a vector. The "##$" is a regular expression that says match if ## are the last two characters, the "$". anchors the ## to the end.