From: Josselin <josselin@...>
Date: 2007-05-04T01:40:05+09:00
Subject: Re: array slicing

On 2007-05-03 17:38:57 +0200, "Raf Coremans" <rrafje@gmail.com> said:

> 2007/5/3, Josselin <josselin@wanadoo.fr>:
>> given an array
>> 
>> anArray = [["a", 1, 1], ["b", 1, 2], ["c", 1, 5], ["z", 1, 1], ["e", 1,
>> 5], ["f", 1, 6], ["g", 1, 1], ["h", 1, 3], ["i", 1, 1], ["j", 1, 2],
>> ["k", 1, 1], ["y", 1, 6], ["m", 1, 1], ["u", 1, 2], ["v", 1, 1], ["p",
>> 1, 4], ["q", 1, 5], ["r", 1, 1], ["n", 1, 1], ["t", 2, 3], ["s", 2, 2],
>> ["o", 2, 1], ["w", 2, 1], ["x", 2, 1], ["l", 2, 1], ["d", 2, 1]]
>> 
>> I would like to get it  sliced in groups of element having the same 2nd
>> and 3rd values
>> 
>> sliced_array = [
>> [ ["a", 1, 1],["g", 1, 1], ["i", 1, 1], ["k", 1, 1], ["m", 1, 1], ["n",
>> 1, 1],["r", 1, 1],["v", 1, 1],["z", 1, 1] ],
>>  [ ["b", 1, 2],["j", 1, 2], ["u", 1, 2] ],
>> [ ["c", 1, 5],["e", 1, 5],["q", 1, 5] ],
>> [ ["d", 2, 1],["l", 2, 1], ["l", 2, 1], ["o", 2, 1],["w", 2, 1],["x", 2, 1] ],
>> [ ["f", 1, 6],["y", 1, 6] ],
>> [ ["h", 1, 3] ],
>> [ ["p", 1, 4] ],
>> [ ["s", 2, 2] ],
>> [ ["t", 2, 3] ]
>>  ]
> 
> Applying a trick I learned today:
> 
> anArray.inject( Hash.new{ |hash, key| hash[key] =[] } ){ |hash,
> subarray| hash[subarray[1, 2]] << subarray; hash }.values
> 
> Or if you need a sorted result:
> 
> anArray.inject( Hash.new{ |hash, key| hash[key] =[] } ){ |hash,
> subarray| hash[subarray[1, 2]] << subarray; hash }.values.sort_by{
> |subarray| subarray[0][1,2] }
> 
> 
> Best regards,
> Raf

good to know , what about the partition_by , it seems simple ?

module Enumerable
  def partition_by
    r = Hash.new{ |h,k| h[k]=[] }
    each do |e|
      r[ yield(e) ] << e
    end
    return r
  end
end

And then :

require 'enumerator'
sArray = anArray.sort_by {|item| [item[1], item[2] ] }

sArray.partition_by {|ary| ary[1..2]}.to_enum(:each_value).to_a=> 
[[["j", 1, 2], ["u", 1, 2], ["b", 1, 2]], [["l", 2, 1], ["x", 2, 1], 
["o", 2, 1], ["w", 2, 1], ["d", 2, 1]], [["a", 1, 1], ["z", 1, 1], 
["v", 1, 1], ["r", 1, 1], ["i", 1, 1], ["m", 1, 1], ["g", 1, 1], ["k", 
1, 1], ["n", 1, 1]], [["f", 1, 6], ["y", 1, 6]], [["t", 2, 3]], [["c", 
1, 5], ["e", 1, 5], ["q", 1, 5]], [["s", 2, 2]], [["p", 1, 4]], [["h", 
1, 3]]]

and that's it.....