string starting with specific pattern

Question

This is very simple R question but I could not find an answer.

I would like to find strings starting with a specific pattern. e.g. if I have the pattern \"ABC

Answer 1

Regex is simpler in this case:

grepl("^ABC", x)
[1]  TRUE FALSE FALSE

The caret ^ special character identifies the beginning of the line. No need to have to specify the amount of characters to count to.

Answer 2

You could use substr for this:

test <- c("ABCGDFGFD","WWABC","AYBC")

substr(test, 1, 3) == 'ABC'

[1]  TRUE FALSE FALSE

If it needs to be longer or shorter, you can change the arguments in substring from 1 and 3. With 1 and 3, it starts at the beginning of each string, and looks up to, and including, the third character.