From: Rob Biedenharn <Rob@...>
Date: 2009-03-19T01:31:22+09:00
Subject: Re: Complex sort of matrix possible, e.g. like Excel?

On Mar 18, 2009, at 1:58 AM, Christopher Dicely wrote:

> Enumerable#sort lets you do this fairly easily with just a pure array
> of arrays, e.g., to sort the array-of-arrays "arr" by the first column
> ascending and the second descending:
>
> arr.sort {|a,b| [a[0]<=>b[0], b[1]<=>a[1]].find {|x| x!=0} || 0}

Not to detract to much from the other responses, but this ought to be:

arr.sort {|a,b| (a[0] <=> b[0]).nonzero? || b[1] <=> a[1] }

Take a look at what Numeric#nonzero? does.  The docs specifically  
mention its use when chaining comparisons this way.

Doing arr.sort_by {|a| [a[0], -a[1]] } only works if the second  
element responds to @- (like any Numeric would, but certainly not  
String).

-Rob

> On 3/17/09, RichardOnRails <RichardDummyMailbox58407@uscomputergurus.com 
> > wrote:
>> Hi,
>>
>> I've got an array of rows (and thus a matrix) created user FasterCSV
>> to extract data from a CSV file.  I'd like to sort the matrix on
>> column A ascending and, within that, column B descending.  I looked  
>> at
>> Matrix,  but it doesn't seem to address that functionality.  Is there
>> a package that does, or do I have to write my own SuperMatrix
>> inherited from Matrix?
>>
>> Thanks in Advance,
>> Richard

Rob Biedenharn		http://agileconsultingllc.com
Rob@AgileConsultingLLC.com