From: "David A. Black" <dblack@...>
Date: 2008-04-30T05:37:46+09:00
Subject: Re: Getting array index for non-zero elements

Hi --

On Wed, 30 Apr 2008, Siep Korteling wrote:

> Rob Biedenharn wrote:
>> On Apr 29, 2008, at 3:46 PM, Victor Reyes wrote:
>>
>>>            [5,0,0,4,0,6,0,3,0],
>>> # Output: 0 0 0 0 1 9 0 4 0
>>>          puts
>>> nonzeroIndex
>>>                                                           #
>>> Output: *nil*
>>>
>>> Any help will be greatly appreciated, as usual!
>>>
>>> Thank you
>>>
>>> Victor
>>
>>
>>
>> irb> require 'code/ruby/ext/enumerable.rb'
>> => true
>> irb> @ga[0]
>> => [0, 0, 0, 0, 1, 9, 0, 4, 0]
>> irb> @ga[0].map_with_index {|e,i| e.zero? ? nil : i}
>> => [nil, nil, nil, nil, 4, 5, nil, 7, nil]
>> irb> @ga[0].map_with_index {|e,i| e.zero? ? nil : i}.compact
>> => [4, 5, 7]
>>
>> Then you just need Enumerable#map_with_index
>>
>> module Enumerable
>>    # Like each_with_index, but the value is the array of block results.
>>    def map_with_index
>>      a = []
>>      each_with_index { |e,i| a << yield(e, i) }
>>      a
>>    end
>> end
>>
>> -Rob
>>
>> Rob Biedenharn    http://agileconsultingllc.com
>> Rob@AgileConsultingLLC.com
>
> It works without the 'require' here.(VERSION=1.8.6). I like the
> map_with_index method (new for me), but isn't it overkill here?
>
> @ga.each do |sub_arr|
>    sub_arr.each_with_index do |value,index|
>       print index.to_s + " " unless value == 0
>    end
>    puts
> end

If all you need is side-effects, like printing, then you can used
#each (with_ or without index). #map_with_index, like #map itself,
returns a second collection.


David

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