From: Jenda Krynicky <jenda@...>
Date: 2007-03-16T00:14:42+09:00
Subject: Re: non-destructive merging of hashes in array

Giles Bowkett wrote:
> Hi, I have an array of hashes. The keys in the hashes represent the same 
> things.
> 
> eg:
> 
> h1 = {:rabbits => 5}
> h2 = {:rabbits => 10}
> 
> bunnies = [h1, h2]
> 
> I want to end up with this:
> 
> {:rabbits => 15}

res = Hash.new(0) # to give the new keys a sensible default
bunnies.each {|arr| arr.each { | key, value | res[key] += value }}

P.S.: I thought about
res = {}
bunnies.each {|arr| arr.each { | key, value | (res[key]||=0) += value }}

but (res[key]||=0) is not a lvalue. It was even considered a syntax 
error with the helpfull error message of:

   syntax error, unexpected tOP_ASGN, expecting '}'

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