if @a = (1,2,3), then undef @a[1,2] is proper, undefines $a[2]
just undef @b[2], is giving me @b's 0 ,1 and 2 indexes to be undef.
if %hash = qw(a b c d) then  undef @hash{qw(a c)} is proper, undefines only $hash{c}
just undef @hash1{qw(a c}} is giving me the values of the keys a and c to be undef