From: Ryan Davis <ryand-ruby@...>
Date: 2009-10-02T04:21:49+09:00
Subject: Re: how do you do this


On Oct 1, 2009, at 05:34 , Ilan Berci wrote:

> George George wrote:
>> Given an array of strings e.g.
>> x = ["abc","abcde" "def","xyzwj"] and of different lengths,
>> how can you efficiently create new arrays of strings which are of the
>> same length. for example the above array can be transformed into
>>
>> x1 = ["abc","def"]
>> x2 = ["abcde","xyzwj"]
>>
>> Thank you.
>
> y = {}
> x.each do |v|
>  y[v.length] || = []
>  y[v.length] << v
> end
> y.values
>
> or if you prefer less lines..
>
> x.inject({}) do |h, v|
>  (y[v.length] || = []) << v
>  h
> end.values

Syntax error in both cases. It needs to be "||=", not "|| =".

Well... inject ALWAYS loses, but fanboys sure seems to like it for no  
good reason.

By using better names and the right tool for the job, this becomes a  
LOT more readable, maintanable, and faster all in one fell swoop:

by_length = Hash.new { |h,k| h[k] = [] }
strings.each do |string|
   by_length[string.length] << string
end
by_length.values # I think this part is a mistake, but I wanted to match

I think the readability is more important than speed by a long shot...  
But just in case you're not convinced, check out the benchmarks:

% ./blah.rb 10000
# of iterations = 10000
                           user     system      total        real
null_time             0.000000   0.000000   0.000000 (  0.001370)
mine                  7.790000   0.050000   7.840000 (  7.869737)
yours-inject         15.170000   0.050000  15.220000 ( 15.554334)
yours-each           11.850000   0.100000  11.950000 ( 12.013553)

inject is twice as slow as mine. stop using it.