From: mortee <mortee.lists@...>
Date: 2007-10-12T12:48:40+09:00
Subject: Re: sort double-dimensional array by column

Mr_Tibs wrote:
> Hi,
> 
> I have a [m X n] double-dimensional array in Ruby and I'm trying to
> sort the entries (rows) by the 6-th column, which is a DateTime
> object. Things get a little bit complicated, since I might have a nil
> value in that column. If that happens, then I want to sort by the 7-th
> column.
> This is what I have so far:
> 
> cset_arr = cset_arr.sort do |x, y|
>          if x[5].nil? && y[5].nil?
>                  x[6] <=> y[6]
>          elsif x[5].nil? && !y[5].nil?
>                  y[5] # ???
>          elsif !x[5].nil? && y[5].nil?
>                  x[5] # ???
>          elsif !x[5].nil? && !y[5].nil?
>                  x[5] <=> y[5]
>          end
> end

What about this one?

cset_arr.sort_by{|row| [ row[5] || DateTime.new, row[6] ] }

Comparing two arrays returns the comparison of the first differing pair
of respective elements. DateTime.new returns some value far in the past,
I guess the lowest possible value. So if both dates are nil, then the
first value in the sort key become the same (this default DateTime
value), thus the 7th column gets compared. Otherwise nil gets replaced
by a value which is most probably lower than any meaningful one.

mortee