in reply to need an array ref from grep

Don't use \, use []

my $arr_ref = [ grep /[[:alpha:]]/, keys %h ] ;

jeffa

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)