From: Stefan Rusterholz <apeiros@...>
Date: 2007-08-25T06:40:51+09:00
Subject: Re: Combining Array Elements

Greg Kujawa wrote:
> On Aug 24, 9:52 am, "Robert Klemme" <shortcut...@googlemail.com>
> wrote:
>> > > [["Value A", "Value B", 3], ["Value A", "Value C", 2],["Value A",
>> > > that will suit the task?
>> > "Value B", 1]]
>> > hash[ elem[0,2] ] += elem[2]; hash }.collect { |k, v|  k + [v] }
>> => {["Value A", "Value C"]=>2, ["Value A", "Value B"]=>4}
>> irb(main):007:0> arr.inject(Hash.new(0)) {|ha,(a,b,c)|
>> ha[[a,b]]+=c;ha}.map {|x| x.flatten}
>> => [["Value A", "Value C", 2], ["Value A", "Value B", 4]]
>>
>> At least 1 #inject. :-)
>>
>> Kind regards
>>
>> robert- Hide quoted text -
>>
>> - Show quoted text -
> 
> Thanks guys. All of the insight helps me out tremendously. There are a
> lot of abilities that I never tapped into along these lines. Great
> stuff and hopefully more tools in my belt. Appreciate the tips!

What makes me slightly sad is that all those examples try to squeeze as 
much as possible into a single statement. Frankly, in my opinion the 
resulting code is horrible to read again a few months later.
I'll try to go a different way, a bit more to type but hopefully easier 
to read. Maybe somebody has an even more readable idea.

array  = [["Value A", "Value B", 3], ["Value A", "Value C", 2],["Value 
A", "Value B", 1]]
groups = array.group_by { |element| element.first(2) }
result = groups.map { |key, values|
  values.map! { |a,b,c| c } # if I knew what each value represents I'd 
chose better names
  key+[values.sum]
}

# required code (group_by is in 1.9, though probably a different 
implementation, sum is in activesupport afaik)
module Enumerable
  def group_by(result=nil, add=nil)
    result ||= Hash.new { |h,k| h[k]=[] }
    add    ||= :<<
    each { |args| result[yield(args)].__send__(add, args) }
    result
  end
end

module Enumerable
  def sum
    inject(0) { |a,b| a+b }
  end
end

Regards
Stefan
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