How to merge hashes if a specified key's values are same in a array

Question

I have a array of hashes like this:

[ {:foo=>2, :date=>Sat, 01 Sep 2014},
 {:foo2=>2, :date=>Sat, 02 Sep 2014},
 {:foo3=>3, :date=>Sat, 01 Sep 2014},
 {:foo4=>4, :date=>Sat, 03 Sep 2014},
  {:foo5=>5, :date=>Sat, 02 Sep 2014}]

And I want to merge hashes if the :date are same. What I expect from the array above is:

[ {:foo=>2, :foo3=>3, :date=>Sat, 01 Sep 2014},
 {:foo2=>2, :foo5=>5 :date=>Sat, 02 Sep 2014},
 {:foo4=>4, :date=>Sat, 03 Sep 2014}]

How can I do it?

Maybe should I reconsider data structure itself? For example should I use date value as a key of hash?

Answer 1

Here's how you could do it in a line (demo):

hashes.group_by{|h| h[:date] }.map{|_, hs| hs.reduce(:merge)}

This code does the following:

• groups all hashes by their :date value
• for each :date group, takes all hashes in it and merges them all into one hash

EDIT: Applied modifications suggested by tokland and Cary Swoveland. Thanks!