Re: Complex sort of matrix possible, e.g. like Excel?

On Mar 19, 8:57=A0pm, RichardOnRails
<[e-mail]> wrote:
> On Mar 19, 5:18=A0pm, Rob Biedenharn <[e-mail]>
> wrote:
>
>
>
> > On Mar 19, 2009, at 4:42 PM, RichardOnRails wrote:
>
> > > On Mar 18, 12:31 pm, Rob Biedenharn <[e-mail]>
> > > wrote:
> > >> On Mar 18, 2009, at 1:58 AM, Christopher Dicely wrote:
>
> > >>> Enumerable#sort lets you do this fairly easily with just a pure =A0
> > >>> array
> > >>> of arrays, e.g., to sort the array-of-arrays "arr" by the first =A0
> > >>> column
> > >>> ascending and the second descending:
>
> > >>> arr.sort {|a,b| [a[0]<=3D>b[0], b[1]<=3D>a[1]].find {|x| x!=3D0} ||=
 0}
>
> > >> Not to detract to much from the other responses, but this ought to =
=A0
> > >> be:
>
> > >> arr.sort {|a,b| (a[0] <=3D> b[0]).nonzero? || b[1] <=3D> a[1] }
>
> > >> Take a look at what Numeric#nonzero? does. =A0The 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 =A0
> > >>> <[e-mail]
> > >>>> wrote:
> > >>>> Hi,
>
> > >>>> I've got an array of rows (and thus a matrix) created user =A0
> > >>>> FasterCSV
> > >>>> to extract data from a CSV file. =A0I'd like to sort the matrix on
> > >>>> column A ascending and, within that, column B descending. =A0I loo=
ked
> > >>>> at
> > >>>> Matrix, =A0but it doesn't seem to address that functionality. =A0I=
s =A0
> > >>>> there
> > >>>> a package that does, or do I have to write my own SuperMatrix
> > >>>> inherited from Matrix?
>
> > >>>> Thanks in Advance,
> > >>>> Richard
>
> > >> Rob Biedenharn =A0 =A0 =A0 =A0 =A0http://agileconsultingllc.com
> > >> [e-mail]
>
> > > On Mar 18, 12:31 pm, Rob Biedenharn <[e-mail]>
> > > wrote:
> > >> On Mar 18, 2009, at 1:58 AM, Christopher Dicely wrote:
>
> > >>> Enumerable#sort lets you do this fairly easily with just a pure =A0
> > >>> array
> > >>> of arrays, e.g., to sort the array-of-arrays "arr" by the first =A0
> > >>> column
> > >>> ascending and the second descending:
>
> > >>> arr.sort {|a,b| [a[0]<=3D>b[0], b[1]<=3D>a[1]].find {|x| x!=3D0} ||=
 0}
>
> > >> Not to detract to much from the other responses, but this ought to =
=A0
> > >> be:
>
> > >> arr.sort {|a,b| (a[0] <=3D> b[0]).nonzero? || b[1] <=3D> a[1] }
>
> > >> Take a look at what Numeric#nonzero? does. =A0The 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 =A0
> > >>> <[e-mail]
> > >>>> wrote:
> > >>>> Hi,
>
> > >>>> I've got an array of rows (and thus a matrix) created user =A0
> > >>>> FasterCSV
> > >>>> to extract data from a CSV file. =A0I'd like to sort the matrix on
> > >>>> column A ascending and, within that, column B descending. =A0I loo=
ked
> > >>>> at
> > >>>> Matrix, =A0but it doesn't seem to address that functionality. =A0I=
s =A0
> > >>>> there
> > >>>> a package that does, or do I have to write my own SuperMatrix
> > >>>> inherited from Matrix?
>
> > >>>> Thanks in Advance,
> > >>>> Richard
>
> > >> Rob Biedenharn =A0 =A0 =A0 =A0 =A0http://agileconsultingllc.com
> > >> [e-mail]
>
> > > Hi Rob,
>
> > > Thanks for your response. =A0I don't want to be an expert on sorting
> > > matrices. =A0I 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 =3D []
> > > FasterCSV.foreach(selectedCsvFile, :headers =3D> false) do |row|
> > > =A0 =A0matrix << row
> > > end
>
> > > I want (in Excel terms) the matrix sorted on column B asc. and within
> > > that col. I asc. =A0Both columns are textual. =A0Based on your guidan=
ce, I
> > > added the line:
>
> > > sortedMatrix =3D matrix.sort {|a,b| [a[1]<=3D>b[1], a[8] <=3D> 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. =A0Any ideas.
>
> > > Best wishes,
> > > Richard
>
> > Well, my guidance was:
> > =A0 =A0arr.sort {|a,b| (a[0] <=3D> b[0]).nonzero? || b[1] <=3D> a[1] }
>
> > Which translates to your:
> > =A0 =A0sortedMatrix =3D matrix.sort {|a,b| (a[1]<=3D>b[1]).nonzero? || =
a[8] =A0
> > <=3D> b[8] }
>
> > You might also need:
> > =A0 =A0matrix << row.to_a
> > or
> > =A0 =A0matrix << row.fields
> > in your loop, but a FasterCSV::Row probably behaves sufficiently like =
=A0
> > an Array to sort properly. Whether it continues to behave later (when =
=A0
> > you *really* need an Array), may resolve the question of whether you =
=A0
> > need to call #to_a or #fields on your row.
>
> > Real code will always get you a better answer that pseudo-code.
>
> > If you meant for either sort on Col.B or Col.I to be *descending*, =A0
> > then swap the a and b in the appropriate expression. (Your original =A0
> > question had the secondary sort descending, but the latest [with =A0
> > code ;-)] says "col. I asc.")
>
> > -Rob
>
> > Rob Biedenharn =A0 =A0 =A0 =A0 =A0http://agileconsultingllc.com
> > [e-mail]
>
> Rob,
>
> Thank you very much for hanging in there with me until the fog lifted.
> I thought about your advice and managed to mangle it. =A0If I hadn't
> been such a "wise guy", =A0I could have translated your original advice
> as you did and been on my way.
>
> Regarding the asc/desc on the I col., =A0I changed my mind midway and
> decided my app requires asc. on I.
>
> But I have a final question: =A0I thought your expression had a flaw
> because, in my view, =A0"(a[1]<=3D>b[1]).nonzero?", if true, should cause
> the block to return true rather than plus or minus.
>
> So I concocted:
> sortedMatrix =3D matrix.sort {|a,b| (v =3D a[1]<=3D>b[1]).nonzero? ? v : =
(a
> [8] <=3D> b[8] )}
> which works.
>
> But yours works, too. =A0So my understanding of how block evaluation
> works when invoked by a calling function is flawed.
>
> Do you have a simple explanation of the flaw in my thinking, =A0or can
> you point me to a relevant online tutorial on this? =A0But don't trouble
> yourself on this; it's only icing on the cake.
>
> Thank you very much for the pains you took to get me going again.
>
> Very best wishes,
> Richard

OK Rob,

I Googled "Ruby nonzero? (thus doing essentially what you suggest in
your original response).  And I see that when the expression is
processed by nonzero?,  the latter returns NOT true or false,  but
rather non-zero value or nil (which is almost 'false').  Cool!

So my extra "v" is documented to be superfluous :-)

Again, many thanks for your generous and excellent guidance.

Best wishes,
Richard