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

ruby-talk
1

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

2

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}

···

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

3

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.

···

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?

4

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

···

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}

--
remember.guy do |as, often| as.you_can - without end

5

Hey Christopher,

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

Best wishes,
Richard

···

On Mar 18, 1:58 am, Christopher Dicely <cmdic...@gmail.com> 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}

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

6

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

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

7

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

···

On Mar 19, 2009, at 10:44 PM, Ryan Davis wrote:

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.

8

Hi Robert,

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

Best wishes,
Richard

···

On Mar 18, 6:16 am, Robert Klemme <shortcut...@googlemail.com> wrote:

2009/3/18 Christopher Dicely <cmdic...@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

--
remember.guy do |as, often| as.you_can - without end

9

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

···

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]]}

10

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 :slight_smile:

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

···

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

11

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.

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

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?

:smiley:

···

On Mar 19, 2009, at 20:01 , Rob Biedenharn wrote:

On Mar 19, 2009, at 10:44 PM, Ryan Davis wrote:

12

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

···

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]] }

--
remember.guy do |as, often| as.you_can - without end

13

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

···

On Mar 19, 2009, at 4:42 PM, RichardOnRails wrote:

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 :slight_smile:

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

14

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.

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

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?

:smiley:

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.

- "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

···

On Mar 20, 2009, at 3:27 AM, Ryan Davis wrote:

On Mar 19, 2009, at 20:01 , Rob Biedenharn wrote:

On Mar 19, 2009, at 10:44 PM, Ryan Davis wrote:

15

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

···

On Mar 19, 5:18 pm, Rob Biedenharn <R...@AgileConsultingLLC.com> wrote:

On Mar 19, 2009, at 4:42 PM, RichardOnRails wrote:

> 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 :slight_smile:

> 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

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
R...@AgileConsultingLLC.com

16

I'm kinda surprised nobody has said this:

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

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

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

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

%w( a b c d ).sort_by { |s| -s }

=> ["d", "c", "b", "a"]

%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:

%w( a aa ab bb bbb ).sort {|a,b| b <=> a }

=> ["bbb", "bb", "ab", "aa", "a"]

%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

···

On Mar 20, 2009, at 7:17 AM, Rob Biedenharn wrote:

On Mar 20, 2009, at 3:27 AM, Ryan Davis wrote:

On Mar 19, 2009, at 20:01 , Rob Biedenharn wrote:

On Mar 19, 2009, at 10:44 PM, Ryan Davis wrote:

17

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 :slight_smile:

Again, many thanks for your generous and excellent guidance.

Best wishes,
Richard

···

On Mar 19, 8:57 pm, RichardOnRails <RichardDummyMailbox58...@USComputerGurus.com> wrote:

On Mar 19, 5:18 pm, Rob Biedenharn <R...@AgileConsultingLLC.com> > wrote:

> On Mar 19, 2009, at 4:42 PM, RichardOnRails wrote:

> > 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 :slight_smile:

> > 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

> 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
> 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

18

Richard,

Glad to have helped.

-Rob

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

···

On Mar 19, 2009, at 9:22 PM, RichardOnRails wrote:

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 :slight_smile:

Again, many thanks for your generous and excellent guidance.

Best wishes,
Richard