From: Robert Klemme <shortcutter@...>
Date: 2009-08-04T18:48:47+09:00
Subject: Re: How to extract only needed attribute from an array

2009/8/4 Thriving K. <superdisconnect@hotmail.com>:
>
> I have an object called Tags with id and name ==> [ tag.id , tag.name]
>
> | [1 , aaa]   |
>
> | [ 3 , bbb]  |
>
> | [ 5 , ccc]  |
>
> | [ 6 , dfd]  |
>
> | [ 7 , waf]  |
>
> | [ 11 , vee] |
>
> There is an array with the list of tags , i just want to extract all
> tag.id
> as a new array, what is the easiest way to do

In any case you need method #map.  In 1.9* you can even do use map(&:id):

irb(main):001:0> Tag = Struct.new :id, :name
=> Tag
irb(main):002:0> a = Array.new(5) {|i| Tag.new(i, "n"*i)}
=> [#<struct Tag id=0, name="">, #<struct Tag id=1, name="n">,
#<struct Tag id=2, name="nn">, #<struct Tag id=3, name="nnn">,
#<struct Tag id=4, name="nnnn">]
irb(main):003:0> a.map(&:id)
=> [0, 1, 2, 3, 4]

Kind regards

robert


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