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

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31fdda5f38fc6df4e193cfb7445ddc5a?d=identicon&s=25 RichardOnRails (Guest)
on 2009-03-18 06:05
(Received via mailing list)
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
D7463bd611f227cfb2ef4da4a978a203?d=identicon&s=25 Christopher Dicely (Guest)
on 2009-03-18 07:01
(Received via mailing list)
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}
E0d864d9677f3c1482a20152b7cac0e2?d=identicon&s=25 Robert Klemme (Guest)
on 2009-03-18 11:19
(Received via mailing list)
2009/3/18 Christopher Dicely <cmdicely@gmail.com>:
> 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}

Alternatively with less intermediate Arrays and less comparison
operations.

arr.sort do |a,b|
 c = a[0]<=>b[0]
 c == 0 ? b[1]<=>a[1] : c
end

You can as well do

arr.sort_by {|a,b| [a[0]<=>b[0], b[1]<=>a[1]]}

Cheers

robert
31fdda5f38fc6df4e193cfb7445ddc5a?d=identicon&s=25 RichardOnRails (Guest)
on 2009-03-18 15:26
(Received via mailing list)
On Mar 18, 1:58 am, Christopher Dicely <cmdic...@gmail.com> wrote:
> > 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
>
>

Hey Christopher,

That's perfect!  I had faith that the community had dealt with this
issue.

Best wishes,
Richard
31fdda5f38fc6df4e193cfb7445ddc5a?d=identicon&s=25 RichardOnRails (Guest)
on 2009-03-18 15:27
(Received via mailing list)
On Mar 18, 6:16 am, Robert Klemme <shortcut...@googlemail.com> wrote:
> arr.sort do |a,b|
> robert
>
> --
> remember.guy do |as, often| as.you_can - without end

Hi Robert,

As usual, you've got the perfect answer.  Thank you very much.

Best wishes,
Richard
E7559e558ececa67c40f452483b9ac8c?d=identicon&s=25 Gary Wright (Guest)
on 2009-03-18 16:45
(Received via mailing list)
On Mar 18, 2009, at 6:16 AM, Robert Klemme wrote:
> You can as well do
>
> arr.sort_by {|a,b| [a[0]<=>b[0], b[1]<=>a[1]]}

This doesn't seem quite right to me.  Shouldn't it be:

arr.sort_by { |item| [item[0], item[1]] }

sort_by will use Array#<=> to compare the two element
array and Array#<=> simply uses <=> on each element.

Gary Wright
E0d864d9677f3c1482a20152b7cac0e2?d=identicon&s=25 Robert Klemme (Guest)
on 2009-03-18 17:02
(Received via mailing list)
2009/3/18 Gary Wright <gwtmp01@mac.com>:
>
> On Mar 18, 2009, at 6:16 AM, Robert Klemme wrote:
>>
>> You can as well do
>>
>> arr.sort_by {|a,b| [a[0]<=>b[0], b[1]<=>a[1]]}
>
> This doesn't seem quite right to me.  Shouldn't it be:
>
> arr.sort_by { |item| [item[0], item[1]] }

Yes, you're right.  Copy & paste error.  However, your solution is not
fully correct either because it does not take into consideration that
order of the second column should be reversed.  So you'd have to do

arr.sort_by { |item| [item[0], -item[1]] }

Thanks for the heads up!

robert
Ef3aa7f7e577ea8cd620462724ddf73b?d=identicon&s=25 Rob Biedenharn (Guest)
on 2009-03-18 17:35
(Received via mailing list)
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

>> inherited from Matrix?
>>
>> Thanks in Advance,
>> Richard

Rob Biedenharn    http://agileconsultingllc.com
Rob@AgileConsultingLLC.com
31fdda5f38fc6df4e193cfb7445ddc5a?d=identicon&s=25 RichardOnRails (Guest)
on 2009-03-19 21:45
(Received via mailing list)
On Mar 18, 12:31 pm, Rob Biedenharn <R...@AgileConsultingLLC.com>
wrote:
> arr.sort {|a,b| (a[0] <=> b[0]).nonzero? || b[1] <=> a[1] }
> > On 3/17/09, RichardOnRails <RichardDummyMailbox58...@uscomputergurus.com
>
> >> Thanks in Advance,
> >> Richard
>
> Rob Biedenharn          http://agileconsultingllc.com
> R...@AgileConsultingLLC.com

On Mar 18, 12:31 pm, Rob Biedenharn <R...@AgileConsultingLLC.com>
wrote:
> arr.sort {|a,b| (a[0] <=> b[0]).nonzero? || b[1] <=> a[1] }
> > On 3/17/09, RichardOnRails <RichardDummyMailbox58...@uscomputergurus.com
>
> >> 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
Ef3aa7f7e577ea8cd620462724ddf73b?d=identicon&s=25 Rob Biedenharn (Guest)
on 2009-03-19 22:21
(Received via mailing list)
On Mar 19, 2009, at 4:42 PM, RichardOnRails wrote:
>>> arr.sort {|a,b| [a[0]<=>b[0], b[1]<=>a[1]].find {|x| x!=0} || 0}
>> element responds to @- (like any Numeric would, but certainly not
>>>> FasterCSV
>>
>>> column
>> mention its use when chaining comparisons this way.
>>>> Hi,
>>
>
> added the line:
>
> Best wishes,
> Richard


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

Which translates to your:
   sortedMatrix = matrix.sort {|a,b| (a[1]<=>b[1]).nonzero? || a[8]
<=> b[8] }

You might also need:
   matrix << row.to_a
or
   matrix << row.fields
in your loop, but a FasterCSV::Row probably behaves sufficiently like
an Array to sort properly. Whether it continues to behave later (when
you *really* need an Array), may resolve the question of whether you
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*,
then swap the a and b in the appropriate expression. (Your original
question had the secondary sort descending, but the latest [with
code ;-)] says "col. I asc.")

-Rob

Rob Biedenharn    http://agileconsultingllc.com
Rob@AgileConsultingLLC.com
31fdda5f38fc6df4e193cfb7445ddc5a?d=identicon&s=25 RichardOnRails (Guest)
on 2009-03-20 02:00
(Received via mailing list)
On Mar 19, 5:18 pm, Rob Biedenharn <R...@AgileConsultingLLC.com>
wrote:
> >>> of arrays, e.g., to sort the array-of-arrays "arr" by the first  
> >> Take a look at what Numeric#nonzero? does.  The docs specifically
> >>>> wrote:
> >>>> inherited from Matrix?
>
>
>
> >>>> Matrix,  but it doesn't seem to address that functionality.  Is  
> > Hi Rob,
> > end
>
> Which translates to your:
> need to call #to_a or #fields on your row.
> Rob Biedenharn          http://agileconsultingllc.com
> R...@AgileConsultingLLC.com

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.  If I hadn't
been such a "wise guy",  I could have translated your original advice
as you did and been on my way.

Regarding the asc/desc on the I col.,  I changed my mind midway and
decided my app requires asc. on I.

But I have a final question:  I thought your expression had a flaw
because, in my view,  "(a[1]<=>b[1]).nonzero?", if true, should cause
the block to return true rather than plus or minus.

So I concocted:
sortedMatrix = matrix.sort {|a,b| (v = a[1]<=>b[1]).nonzero? ? v : (a
[8] <=> b[8] )}
which works.

But yours works, too.  So 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,  or can
you point me to a relevant online tutorial on this?  But 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
31fdda5f38fc6df4e193cfb7445ddc5a?d=identicon&s=25 RichardOnRails (Guest)
on 2009-03-20 02:25
(Received via mailing list)
On Mar 19, 8:57 pm, RichardOnRails
<RichardDummyMailbox58...@USComputerGurus.com> wrote:
>
>
>
> > >>>> Matrix,  but it doesn't seem to address that functionality.  Is  
> > > On Mar 18, 12:31 pm, Rob Biedenharn <R...@AgileConsultingLLC.com>
>
> > >> String).
> > >>>> to extract data from a CSV file.  I'd like to sort the matrix on
> > >> Rob Biedenharn          http://agileconsultingllc.com
> > > matrix = []
> > > Ruby gave me a syntax error:
> > Well, my guidance was:
> > in your loop, but a FasterCSV::Row probably behaves sufficiently like  
>
> as you did and been on my way.
> [8] <=> b[8] )}
>
> 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
Ef3aa7f7e577ea8cd620462724ddf73b?d=identicon&s=25 Rob Biedenharn (Guest)
on 2009-03-20 03:09
(Received via mailing list)
On Mar 19, 2009, at 9:22 PM, RichardOnRails wrote:

>
> Best wishes,
> Richard


Richard,

Glad to have helped.

-Rob

Rob Biedenharn    http://agileconsultingllc.com
Rob@AgileConsultingLLC.com
5a837592409354297424994e8d62f722?d=identicon&s=25 Ryan Davis (Guest)
on 2009-03-20 03:47
(Received via mailing list)
On Mar 17, 2009, at 22:02 , RichardOnRails wrote:

> 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?

I'm kinda surprised nobody has said this:

     sorted = matrix.sort_by { |row| [row[0], -row[1]] }

P.S. PLEASE trim to the relevant parts when you reply. In some of your
email on this thread you have two whole copies of nearly the whole
thread.
Ef3aa7f7e577ea8cd620462724ddf73b?d=identicon&s=25 Rob Biedenharn (Guest)
on 2009-03-20 04:04
(Received via mailing list)
On Mar 19, 2009, at 10:44 PM, Ryan Davis wrote:
> I'm kinda surprised nobody has said this:
>
>    sorted = matrix.sort_by { |row| [row[0], -row[1]] }
>
> P.S. PLEASE trim to the relevant parts when you reply. In some of
> your email on this thread you have two whole copies of nearly the
> whole thread.


Actually, it was suggested, but it assumes that row[1] has a -@
method.  The OP confirmed later that the columns are text, not numbers.

-Rob

Rob Biedenharn    http://agileconsultingllc.com
Rob@AgileConsultingLLC.com
5a837592409354297424994e8d62f722?d=identicon&s=25 Ryan Davis (Guest)
on 2009-03-20 08:31
(Received via mailing list)
On Mar 19, 2009, at 20:01 , Rob Biedenharn wrote:

> Actually, it was suggested, but it assumes that row[1] has a -@
> method.  The OP confirmed later that the columns are text, not
> numbers.

kk. sorry. I made assumptions based on him using Matrix. I couldn't
see that someone suggested this already through all the noise. :)

umm....

class String
   def -@
     self.gsub(/./) { |s| (?z - s[0] + ?a).chr }
   end
end

 >> %w(abc def ghi jhk).sort_by { |s| -s }
=> ["jhk", "ghi", "def", "abc"]

horrible, no?

:D
Ef3aa7f7e577ea8cd620462724ddf73b?d=identicon&s=25 Rob Biedenharn (Guest)
on 2009-03-20 12:21
(Received via mailing list)
On Mar 20, 2009, at 3:27 AM, Ryan Davis wrote:
>> Actually, it was suggested, but it assumes that row[1] has a -@
>    self.gsub(/./) { |s| (?z - s[0] + ?a).chr }
>  end
> end
>
> >> %w(abc def ghi jhk).sort_by { |s| -s }
> => ["jhk", "ghi", "def", "abc"]
>
> horrible, no?
>
> :D

Only if you have any characters that aren't lowercase letters.

class String
  def -@
    self.gsub(/./) {|s| (255 - s[0]).chr }
  end
end

Well, still pretty horrible, though.

irb> - "Ryan Davis"
=> "\255\206\236\221\337\273\236\211\226\214"

If you ever meet someone with that name, don't shake hands; the
universe could come to an end!

-Rob

Rob Biedenharn    http://agileconsultingllc.com
Rob@AgileConsultingLLC.com
Ef3aa7f7e577ea8cd620462724ddf73b?d=identicon&s=25 Rob Biedenharn (Guest)
on 2009-03-20 12:48
(Received via mailing list)
On Mar 20, 2009, at 7:17 AM, Rob Biedenharn wrote:
>>
>
> class String
> def -@
>   self.gsub(/./) {|s| (255 - s[0]).chr }
> end
> end


Oops, it is horrible because it doesn't reverse sort properly:

irb> %w( a b c d ).sort_by { |s| -s }
=> ["d", "c", "b", "a"]
irb> %w( a b c d ).sort {|a,b| b <=> a }
=> ["d", "c", "b", "a"]

OK when the ordering is based on a letter mismatch, but when one
string is a prefix:

irb> %w( a aa ab bb bbb ).sort {|a,b| b <=> a }
=> ["bbb", "bb", "ab", "aa", "a"]
irb> %w( a aa ab bb bbb ).sort_by { |s| -s }
=> ["bb", "bbb", "a", "ab", "aa"]

Perhaps that's one reason there's no String#-@

-Rob

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