From: "Peña, Botp" <botp@...>
Date: 2007-06-18T11:59:41+09:00
Subject: sorting hash keys and values (was RE: Adding new value (in array) to existing key in a hash)

On Behalf Of Gilbert Lau:
# myhash = {"a" => [[0,0],[3,4]], "b" => [[1,1],[9,8]], "c" => [[7,6]]}
# 
# how do I sort the values to become
# 
# [0,0],[1,1],[3,4],[7,6],[9,8]
# 
# and be able to recall the keys to arrange according to the sorted 
# values, like
# 
# "a", "b", "a", "c", "b"

just be careful w some value clashes

irb(main):112:0> newhash={}
=> {}
irb(main):113:0> myhash.each{|k,v| v.each{|e| newhash[e]=k}}
=> {"a"=>[[0, 0], [3, 4]], "b"=>[[1, 1], [9, 8]], "c"=>[[7, 6]]}

# we create a new hash whose values are now keys 
# (like invert but your case is special)
# so now values still point to their original keys

irb(main):114:0> newhash
=> {[0, 0]=>"a", [1, 1]=>"b", [3, 4]=>"a", [7, 6]=>"c", [9, 8]=>"b"}
irb(main):118:0> newhash.keys
=> [[0, 0], [1, 1], [3, 4], [7, 6], [9, 8]]
irb(main):119:0> newhash.values
=> ["a", "b", "a", "c", "b"]
irb(main):120:0>

there is too much magic in there, i'm not sure how/why ruby sorted it (but i love it :)

anyway, just to be sure

irb(main):145:0> newhash.sort_by{|k,v| k}
=> [[[0, 0], "a"], [[1, 1], "b"], [[3, 4], "a"], [[7, 6], "c"], [[9, 8], "b"]]
irb(main):146:0> newhash.sort_by{|k,v| k}.map{|e| e[0]}
=> [[0, 0], [1, 1], [3, 4], [7, 6], [9, 8]]
irb(main):147:0> newhash.sort_by{|k,v| k}.map{|e| e[1]}
=> ["a", "b", "a", "c", "b"]

kind regards -botp