R maintains the letters vector, so no need to write out entire alphabet.

The function tolower is vectorized, so no need to call sapply (a hidden loop): tolower(unlist(strsplit(s, split=""))).

R's letters only contains 26 elements, so no need to reassign to another object.

R maintains a LETTERS vector, so no need to write out alphabet.

R maintains a letters vector, so need to write out entire alphabet.