Building Hash by grouping array of objects based on a property of the items

Question

I\'m wondering if there is a more canonical way to do this in ruby 1.9

I have an array with a bunch of objects and I want to group them into a Hash using a property of e

Answer 1

Phrogz is correct, group_by is there for the taking. Your code contains one of ruby's gotcha's.

aers = %w(a b c d ab bc de abc)
sh = Hash.new([]) # returns the _same_ array everytime the key is not found. 
# sh = Hash.new{|h,v| h[v] = []}  # This one works
p sh, sh.default

aers.each do |aer|
  sh[aer.size] << aer  #modifies the default [] every time
end
p sh, sh.default
p sh[5]

Output

{}
[]
{}
["a", "b", "c", "d", "ab", "bc", "de", "abc"]
["a", "b", "c", "d", "ab", "bc", "de", "abc"]