Getting array index for non-zero elements

Victor_Reyes · 29 April 2008 19:46

Team,

Given multi-dimension array @ga:

    @ga = [
            [0,0,0,0,1,9,0,4,0],
            [0,0,4,8,0,0,6,0,0],
            [7,5,0,0,0,0,0,0,2],
            [0,9,0,1,0,2,0,0,4],
            [0,0,0,0,0,3,0,0,0],
            [5,0,0,4,0,6,0,3,0],
            [8,0,0,0,0,0,0,7,3],
            [0,0,6,0,0,8,4,0,0],
            [0,1,0,2,9,0,0,0,0]
            ]

I am able to find then non-zero elements of a particular row:

# If r = 0
rowArr = @ga[r]
puts rowArr
# Output: 0 0 0 0 1 9 0 4 0

nonzeroElements = rowArr.find_all {|e| e > 0}
puts nonzeroElements #
Output: 1 9 4

However, I don't actually want the elements, I would like to get the index
of those non-zero elements. I tried the following but it fails:

nonzeroIndex = rowArr.index rowArr.find_all {|e| e > 0}
puts
nonzeroIndex #
Output: *nil*

Any help will be greatly appreciated, as usual!

Thank you

Victor

Rob_Biedenharn1 · 29 April 2008 20:11

Team,

Given multi-dimension array @ga:

   @ga = [
           [0,0,0,0,1,9,0,4,0],
           [0,0,4,8,0,0,6,0,0],
           [7,5,0,0,0,0,0,0,2],
           [0,9,0,1,0,2,0,0,4],
           [0,0,0,0,0,3,0,0,0],
           [5,0,0,4,0,6,0,3,0],
           [8,0,0,0,0,0,0,7,3],
           [0,0,6,0,0,8,4,0,0],
           [0,1,0,2,9,0,0,0,0]
           ]

I am able to find then non-zero elements of a particular row:

# If r = 0
         rowArr = @ga[r]
         puts rowArr
# Output: 0 0 0 0 1 9 0 4 0

         nonzeroElements = rowArr.find_all {|e| e > 0}
         puts nonzeroElements #
Output: 1 9 4

However, I don't actually want the elements, I would like to get the index
of those non-zero elements. I tried the following but it fails:

         nonzeroIndex = rowArr.index rowArr.find_all {|e| e > 0}
         puts
nonzeroIndex #
Output: *nil*

Any help will be greatly appreciated, as usual!

Thank you

Victor

require 'code/ruby/ext/enumerable.rb'

=> true

@ga[0]

=> [0, 0, 0, 0, 1, 9, 0, 4, 0]

@ga[0].map_with_index {|e,i| e.zero? ? nil : i}

=> [nil, nil, nil, nil, 4, 5, nil, 7, nil]

@ga[0].map_with_index {|e,i| e.zero? ? nil : i}.compact

=> [4, 5, 7]

Then you just need Enumerable#map_with_index

module Enumerable
   # Like each_with_index, but the value is the array of block results.
   def map_with_index
     a =
     each_with_index { |e,i| a << yield(e, i) }
     a
   end
end

-Rob

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

···

On Apr 29, 2008, at 3:46 PM, Victor Reyes wrote:

Stefano_Crocco · 29 April 2008 20:11

Array#find_all returns an array containing all the elements for which the
block returns true. Since this array is not a member of rowArr, rowArr.index
returns nil.

The simplest way to achieve what you want, in my opinion, is the following:

require 'enumerator'

rowArr.enum_for(:each_index).find_all{|i| rowArr[i] > 0}

This creates an Enumerator (see ri Enumerator and ri enum_for) whose 'each'
method calls rowArr.each_index instead rowArr.each. The block is thus passed
the index of the elements instead of the elements themselves, and the array
returned by findAll will contain the indexes of the items greater than 0.

I hope this helps

Stefano

···

On Tuesday 29 April 2008, Victor Reyes wrote:

However, I don't actually want the elements, I would like to get the index
of those non-zero elements. I tried the following but it fails:
      nonzeroIndex = rowArr\.index rowArr\.find\_all \{|e| e &gt; 0\}
      puts
nonzeroIndex #
Output: *nil*

Siep_Korteling · 29 April 2008 20:31

Rob Biedenharn wrote:

           [5,0,0,4,0,6,0,3,0],
# Output: 0 0 0 0 1 9 0 4 0
         puts
nonzeroIndex
                                                          #
Output: *nil*

Any help will be greatly appreciated, as usual!

Thank you

Victor

> require 'code/ruby/ext/enumerable.rb'
=> true
> @ga[0]
=> [0, 0, 0, 0, 1, 9, 0, 4, 0]
> @ga[0].map_with_index {|e,i| e.zero? ? nil : i}
=> [nil, nil, nil, nil, 4, 5, nil, 7, nil]
> @ga[0].map_with_index {|e,i| e.zero? ? nil : i}.compact
=> [4, 5, 7]

Then you just need Enumerable#map_with_index

module Enumerable
   # Like each_with_index, but the value is the array of block results.
   def map_with_index
     a =
     each_with_index { |e,i| a << yield(e, i) }
     a
   end
end

-Rob

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

It works without the 'require' here.(VERSION=1.8.6). I like the
map_with_index method (new for me), but isn't it overkill here?

@ga.each do |sub_arr|
    sub_arr.each_with_index do |value,index|
       print index.to_s + " " unless value == 0
    end
    puts
end

Regards,

Siep

···

On Apr 29, 2008, at 3:46 PM, Victor Reyes wrote:

--
Posted via http://www.ruby-forum.com/\.

David_A_Black1 · 29 April 2008 20:37

Hi --

···

On Wed, 30 Apr 2008, Siep Korteling wrote:

Rob Biedenharn wrote:

On Apr 29, 2008, at 3:46 PM, Victor Reyes wrote:

           [5,0,0,4,0,6,0,3,0],
# Output: 0 0 0 0 1 9 0 4 0
         puts
nonzeroIndex
                                                          #
Output: *nil*

Any help will be greatly appreciated, as usual!

Thank you

Victor

> require 'code/ruby/ext/enumerable.rb'
=> true
> @ga[0]
=> [0, 0, 0, 0, 1, 9, 0, 4, 0]
> @ga[0].map_with_index {|e,i| e.zero? ? nil : i}
=> [nil, nil, nil, nil, 4, 5, nil, 7, nil]
> @ga[0].map_with_index {|e,i| e.zero? ? nil : i}.compact
=> [4, 5, 7]

Then you just need Enumerable#map_with_index

module Enumerable
   # Like each_with_index, but the value is the array of block results.
   def map_with_index
     a =
     each_with_index { |e,i| a << yield(e, i) }
     a
   end
end

-Rob

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

It works without the 'require' here.(VERSION=1.8.6). I like the
map_with_index method (new for me), but isn't it overkill here?

@ga.each do |sub_arr|
   sub_arr.each_with_index do |value,index|
      print index.to_s + " " unless value == 0
   end
   puts
end

If all you need is side-effects, like printing, then you can used
#each (with_ or without index). #map_with_index, like #map itself,
returns a second collection.

David

--
Rails training from David A. Black and Ruby Power and Light:
   INTRO TO RAILS June 9-12 Berlin
   ADVANCING WITH RAILS June 16-19 Berlin
   INTRO TO RAILS June 24-27 London (Skills Matter)
See http://www.rubypal.com for details and updates!

Victor_Reyes · 30 April 2008 11:44

Hi Team,

First, thank you for all your replies. I truly appreciate each and everyone
of them!
Generally speaking I have problems explaining in writing an idea or what I
intent to do.
But, let me try to explain what I would like to do.

I am trying to implement a sudoku algorithm.
Given an initial set of values which I represent as the following example:

@ga = [
            [0,0,0,0,1,9,0,4,0],
            [0,0,4,8,0,0,6,0,0],
            [7,5,0,0,0,0,0,0,2],
            [0,9,0,1,0,2,0,0,4],
            [0,0,0,0,0,3,0,0,0],
            [5,0,0,4,0,6,0,3,0],
            [8,0,0,0,0,0,0,7,3],
            [0,0,6,0,0,8,4,0,0],
            [0,1,0,2,9,0,0,0,0]
            ]

I use the above array to propagate the given values to a "master" array
which contains ALL the ORIGINAL valid and possible entries for a location.
At the start all numbers from 1..9:
@aa = [

[123456789,123456789,123456789,123456789,123456789,123456789,123456789,123456789,123456789],

[123456789,123456789,123456789,123456789,123456789,123456789,123456789,123456789,123456789]
]

But I don't want to propagate the zeroes (0) from the given array. I use
zeroes (0) for convenience only.
So, for instance, from the given array please notice that there is a one (1)
at location @ga = [0][4].
Knowing the index of that non-zero value (1 in this case) I would then use
the same index on the so called master array to place the 1.
I will then proceed to eliminate all the ones (1) from the same row and
column, since, as I am sure you know, the rule of sudoku only allows a
particular number once in a given row and column.

Well, that's why I need the index, so I can a bit easier manipulate the
arrays and their contents.

Again, thank you for all your help.

Victor

···

On Tue, Apr 29, 2008 at 4:37 PM, David A. Black <dblack@rubypal.com> wrote:

Hi --

On Wed, 30 Apr 2008, Siep Korteling wrote:

Rob Biedenharn wrote:
>
> > On Apr 29, 2008, at 3:46 PM, Victor Reyes wrote:
> >
> > [5,0,0,4,0,6,0,3,0],
> > > # Output: 0 0 0 0 1 9 0 4 0
> > > puts
> > > nonzeroIndex
> > > #
> > > Output: *nil*
> > >
> > > Any help will be greatly appreciated, as usual!
> > >
> > > Thank you
> > >
> > > Victor
> > >
> >
> >
> >
> > > require 'code/ruby/ext/enumerable.rb'
> > => true
> > > @ga[0]
> > => [0, 0, 0, 0, 1, 9, 0, 4, 0]
> > > @ga[0].map_with_index {|e,i| e.zero? ? nil : i}
> > => [nil, nil, nil, nil, 4, 5, nil, 7, nil]
> > > @ga[0].map_with_index {|e,i| e.zero? ? nil : i}.compact
> > => [4, 5, 7]
> >
> > Then you just need Enumerable#map_with_index
> >
> > module Enumerable
> > # Like each_with_index, but the value is the array of block results.
> > def map_with_index
> > a =
> > each_with_index { |e,i| a << yield(e, i) }
> > a
> > end
> > end
> >
> > -Rob
> >
> > Rob Biedenharn http://agileconsultingllc.com
> > Rob@AgileConsultingLLC.com
> >
>
> It works without the 'require' here.(VERSION=1.8.6). I like the
> map_with_index method (new for me), but isn't it overkill here?
>
> @ga.each do |sub_arr|
> sub_arr.each_with_index do |value,index|
> print index.to_s + " " unless value == 0
> end
> puts
> end
>

If all you need is side-effects, like printing, then you can used
#each (with_ or without index). #map_with_index, like #map itself,
returns a second collection.

David

--
Rails training from David A. Black and Ruby Power and Light:
INTRO TO RAILS June 9-12 Berlin
ADVANCING WITH RAILS June 16-19 Berlin
INTRO TO RAILS June 24-27 London (Skills Matter)
See http://www.rubypal.com for details and updates!

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