From: "Abinoam Jr." <abinoam@...>
Date: 2012-01-17T10:05:33+09:00
Subject: Re: uniq with count; better way?

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.

Some benchmark results...

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

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

Abinoam Jr.