Calculate hamming weight with low hamming weight

J, weight 34

+/,#:a.i.

Usage - place the string to be measured in quotes at the end:

   +/,#:a.i.'+/,#:a.i.'
34

Alternatively, taking input from the keyboard (weight 54):

   +/,#:a.i.1!:1[1
hello
21

J (33)

One lower than 34!

+/,#:3 u:

Heavily inspired by this answer, but a hamming weight of one lower.

   +/,#:3 u:'+/,#:3 u:'
33

J, 39

+/,#:a.i:]

This is a function taking one argument. (Or replace ] with the string directly; as Gareth notes, that brings the cost down to 34.)

   +/,#:a.i:] 'hello world'
45
   +/,#:a.i:] '+/,#:a.i:]'
39