From: Yossef Mendelssohn <ymendel@...>
Date: 2007-08-24T22:34:58+09:00
Subject: Re: Combining Array Elements

On Aug 24, 7:50 am, gregarican <greg.kuj...@gmail.com> wrote:
> I have an array that I would like to combine elements. Here's a sample
> array:
>
> [["Value A", "Value B", 3], ["Value A", "Value C", 2],["Value A",
> Value B", 1]]
>
> What I would like to do is find the elements where the first two items
> are the same and then combine the third. The resulting array would
> consist of:
>
> [["Value A", "Value B", 4],["Value A", "Value C", 2]]
>
> This is something that is out in left field in terms of how I've used
> arrays in the past. Anyone know of a quick bit of script I can whip up
> that will suit the task?


irb(main):001:0> orig_array = [["Value A", "Value B", 3], ["Value A",
"Value C", 2],["Value A", "Value B", 1]]
=> [["Value A", "Value B", 3], ["Value A", "Value C", 2], ["Value A",
"Value B", 1]]
irb(main):002:0> hash = Hash.new(0)
=> {}
irb(main):003:0> orig_array.each { |elem|  hash[ elem[0,2] ] +=
elem[2] }
=> [["Value A", "Value B", 3], ["Value A", "Value C", 2], ["Value A",
"Value B", 1]]
irb(main):004:0> hash.collect { |k, v|  k + [v] }
=> [["Value A", "Value C", 2], ["Value A", "Value B", 4]]


or, more concisely


irb(main):001:0> orig_array = [["Value A", "Value B", 3], ["Value A",
"Value C", 2],["Value A", "Value B", 1]]
=> [["Value A", "Value B", 3], ["Value A", "Value C", 2], ["Value A",
"Value B", 1]]
irb(main):002:0> orig_array.inject(Hash.new(0)) { |hash, elem|
hash[ elem[0,2] ] += elem[2]; hash }.collect { |k, v|  k + [v] }
=> [["Value A", "Value C", 2], ["Value A", "Value B", 4]]


--
-yossef