From: Gavin Sinclair <gsinclair@...>
Date: 2003-07-21T15:25:56+09:00
Subject: Re: Proposal: Array#to_h, to simplify hash generation

>
> To me, 'hashify' implies taking an assoc array and converting it to hash
> form (or perhaps the perl-influenced [a, b, c, d] -> {a=>b, c=>d}). I
> still can't think of a name for the useful case :) make_hash, perhaps ..
>
> *(1..10).make_hash {|i| f(i)}
>
> or maybe the complementary hash_to and hash_from, where the block is
> respectively the value and the key for the corresponding array entry :)
>
> martin


I like "make_hash".  We would get more flexibility if "make_hash" insisted
on receiving two values for the block: one for key and one for value.  In
one instance recently, I wanted to map the "filename" part of a data
object to the object itself.  This, I think, is readable:

   map = receipts.make_hash { |r| r.filename, r }

Whereas in my pet case of mapping filename to size, we have

   map = filenames.make_hash { |fn| fn, File.stat(fn).size }

And your example comes out as

   (1..10).make_hash { |i| i, f(i) }

(I don't know why you put the asterix there; Ranges are Enumerable.)

And, of course, the obligitory reference implementation:

  module Enumerable
    def make_hash
      result = {}
      each do |elt|
        key, value = yield(elt)
        result[key] = value
      end
      result
    end
  end


I've raised an RCR for this (#148).

Cheers,
Gavin