From: Ralph Shnelvar <ralphs@...32.com>
Date: 2012-01-17T10:39:40+09:00
Subject: Re: uniq with count; better way?

Abinoam,

Monday, January 16, 2012, 6:05:33 PM, you wrote:

AJ> On Mon, Jan 16, 2012 at 9:22 PM, Abinoam Jr. <abinoam@gmail.com> wrote:
>> On Mon, Jan 16, 2012 at 1:48 PM, Magnus Holm <judofyr@gmail.com> wrote:
>>> On Mon, Jan 16, 2012 at 17:04, Adam Prescott <adam@aprescott.com> wrote:
>>>> On Mon, Jan 16, 2012 at 16:00, Sigurd <cu9ypd@gmail.com> wrote:
>>>>
>>>>> [4,5,6,4,5,6,6,7].inject(Hash.new(0)) {|res, x| res[x] += 1; res }
>>>>>
>>>>
>>>> I think this is a misuse of inject, personally, every time I see it. It's
>>>> harder to read and it doesn't give the feeling of actually "reducing"
>>>> (inject's alias) the array down to one thing. The required `; res` is a
>>>> sign of that. Compare:
>>>>
>>>> [1, 2, 3, 4].inject(5) { |a, b| a + b }
>>>
>>> There's always each_with_object, although it's a little long:
>>>
>>> �[4,5,6,4,5,6,6,7].each_with_object(Hash.new(0)) { |x, res| res[x] += 1 }
>>>
>>
>> I think Magnus Holm is the clearest (IMHO, yes, it's just a taste and
>> humble opinion.).
>>
>> [4,5,6,4,5,6,6,7].each_with_object(Hash.new(0)) {|num, hsh| hsh[num] += 1}
>>
>> Another way (not better) I remember is...
>>
>> Hash[ [4,5,6,4,5,6,6,7].sort.chunk {|n| n}.map {|ix, els| [ix, els.size] } ]
>>
>> See: http://ruby-doc.org/core-1.9.3/Enumerable.html#method-i-chunk
>>
>> It also can be... clearer?!?
>>
>> Hash[ [4,5,6,4,5,6,6,7].group_by {|n| n}.map {|ix, els| [ix, els.size] } ]
>>
>> Perhaps something like this (same as Magnus Holm) just hiding the
>> complexity into the method.
>>
>> class Array
>> �def totalize_to_hash
>> � �hsh = Hash.new(0)
>> � �self.each do |n|
>> � � �hsh[n] += 1
>> � �end
>> � �hsh
>> �end
>> end
>>
>> [4,5,6,4,5,6,6,7].totalize_to_hash
>>
>> Abinoam Jr.

AJ> Some benchmark results...

AJ> n = 100_000
AJ> Benchmark.bm(15) do |b|
AJ>   b.report("Ralph Shneiver:") { n.times { a = [4,5,6,4,5,6,6,7];
AJ> result = Hash.new(0); a.each { |x|  result[x] += 1 }; result} }
AJ>   b.report("Sigurd:")        { n.times {
AJ> [4,5,6,4,5,6,6,7].inject(Hash.new(0)) {|res, x| res[x] += 1; res } } }
AJ>   b.report("Keinich #1")     { n.times { Hash[a.group_by{|n|n}.map{|k,
AJ> v|[k, v.size]}] } }
AJ>   b.report("Keinich #2")     { n.times {
AJ> Hash.new(0).tap{|h|a.each{|n|h[n] += 1}} } }
AJ>   b.report("Magnus Holm:")   { n.times {
AJ> [4,5,6,4,5,6,6,7].each_with_object(Hash.new(0)) { |x, res| res[x] += 1
AJ> } } }
AJ>   b.report("Abinoam #1:")    { n.times { Hash[
AJ> [4,5,6,4,5,6,6,7].sort.chunk {|n| n}.map {|ix, els| [ix, els.size] } ]
AJ> } }
AJ> end

AJ>                      user     system      total        real
AJ> Ralph Shneiver:   0.290000   0.000000   0.290000 (  0.259640)
AJ> Sigurd:          0.320000   0.000000   0.320000 (  0.289873)
AJ> Keinich #1       0.560000   0.000000   0.560000 (  0.497736)
AJ> Keinich #2       0.280000   0.000000   0.280000 (  0.250843)
AJ> Magnus Holm:     0.310000   0.000000   0.310000 (  0.283344)
AJ> Abinoam #1:      1.140000   0.000000   1.140000 (  1.042744)

AJ> Abinoam Jr.

Wow ... thank you!