r - Extract the first (or last) n characters of a string

Question

I want to extract the first (or last) n characters of a string. This would be the equivalent to Excel's LEFT() and RIGHT(). A small example:

# create a string
a <- paste('left', 'right', sep = '')
a
# [1] "leftright"

I would like to produce b, a string which is equal to the first 4 letters of a:

b
# [1] "left"

What should I do?

Answer 1

See ?substr

R> substr(a, 1, 4)
[1] "left"