You can do this:

    Hash[ preferences.map {|k,v| [k.to_sym, v.nonzero? or false]} ]

This preserves the value if it is nonzero.

**Code review**

Note that when you initialize a return variable and then loop over another variable, e.g.

    hsh = {}
    preferences.each do
      #something that updates hsh
    end

A more idiomatic Ruby way to do this is with a `map`, as the answers show. This will in general result in more concise, expressive code.