See strex::str_elems().
str_elems(string, indices, byrow = TRUE)elems(string, indices, byrow = TRUE)
A character vector.
A vector of integerish values. Negative indexing is allowed as
in stringr::str_sub().
Should the elements be organised in the matrix with one row per
string (byrow = TRUE, the default) or one column per string (byrow = FALSE). See examples if you don't understand.