From: RichardOnRails <RichardDummyMailbox58407@...>
Date: 2009-03-20T05:42:24+09:00
Subject: Re: Complex sort of matrix possible, e.g. like Excel?

On Mar 18, 12:31 pm, Rob Biedenharn <R...@AgileConsultingLLC.com>
wrote:
> 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 <RichardDummyMailbox58...@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
> R...@AgileConsultingLLC.com

On Mar 18, 12:31 pm, Rob Biedenharn <R...@AgileConsultingLLC.com>
wrote:
> 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 <RichardDummyMailbox58...@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
> R...@AgileConsultingLLC.com

Hi Rob,

Thanks for your response.  I don't want to be an expert on sorting
matrices.  I just want to get my project working. (Don't we all :-)

Here's the essence of what I've got working, confirmed with debugging
puts'.

matrix = []
FasterCSV.foreach(selectedCsvFile, :headers => false) do |row|
    matrix << row
end

I want (in Excel terms) the matrix sorted on column B asc. and within
that col. I asc.  Both columns are textual.  Based on your guidance, I
added the line:

sortedMatrix = matrix.sort {|a,b| [a[1]<=>b[1], a[8] <=> b[8]]}

Ruby gave me a syntax error:
ProcessExports.rb:130:in `sort': undefined method `>' for [-1,
1]:Array (NoMethodError)

I'm hoping the problem is that I'm invoking Array::Sort rather than
Enumerable::Sort but nothing my deteriorating brain could devise
worked.  Any ideas.

Best wishes,
Richard