This is a quick way around doing a call to str_elems() followed by a call
of apply(..., paste).
str_paste_elems(string, indices, sep = "")A character vector.
A vector of integerish values. Negative indexing is allowed as
in stringr::str_sub().
A string. The separator for pasting string elements together.
A character vector.
Elements that don't exist e.g. element 5 of "abc" are ignored.