From: Paul <tester.paul@...>
Date: 2007-03-20T06:05:07+09:00
Subject: Re: Sorting Dates and Times in an array

On Mar 19, 4:43 pm, "Phrogz" wrote:
>
> a) Ruby doesn't have multi-dimensional arrays in the core. Unless
> you're using something like NArray, I suspect you're thinking of
> arrays of arrays. In this case, your problem is 'just coding' - if you
> want to sort an array of arrays, you can sort the primary axis and
> then the subsequent arrays. Or you can choose to transpose the array
> and sort along some other array.

Maybe I am thinking of that.. I don't know that terminology.  I
understand a multi-dimensional array, but haven't heard of an "array
of arrays" before.  They sound the same to me.  I'll go with your
phrase. =)

>
> b) Replace the contents? Perhaps you really want map! to convert the
> contents of the array in-place, and then to sort_by{} to twiddle the
> bits.
>
> Or, use less memory and more CPU by using sort!. (It's generally easy
> in computer programming to trade memory for calculation speed, in both
> directions.)

Okay, so I don't know what the difference is between these two:

> @data.sort! { |a,b| b[x].to_f <=> a[x].to_f }     # i.e. descending numeric sort
and
> @data.replace( @data.sort { |a,b| b[x].to_f <=> a[x].to_f } )     # i.e. descending numeric sort

Does the former use more CPU and less memory, and the latter the
opposite?

When I checked the Programming Ruby reference it says that Array#map!
is a 'synonym for Array#collect!' and when I check Array#collect! I
don't think it's what I want in this sort function.  Or if it is, I
don't know how to write the code for it.  And until today I had never
seen 'sort_by' so I'm still trying to figure out that function too.