# Array question - How dynamic is dynamic? **URL:** \ **Category:** Ruby\ **Created:** [April 7, 2009, 2:52pm UTC](https://www.ruby-forum.com/t/array-question-how-dynamic-is-dynamic/164927 "2009-04-07T14:52:15Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![rubina](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e47c2d/32.png) [@rubina](https://www.ruby-forum.com/u/rubina)\ **Post date:** [April 7, 2009, 2:52pm UTC](https://www.ruby-forum.com/t/array-question-how-dynamic-is-dynamic/164927/1 "2009-04-07T14:52:15Z")
Hello all you happy people! I have been thinking about asking this question but did not know how to start. So, if my question is ambiguous please let me know and I will try to make it clearer. Given an NxN array or even an NxM array mA from which at times I break it into sub arrays, I would like to be able to manipulate the sub arrays and have the changes dynamically propagated to the main array mA. For example, assume I have main array mA as listed below. From mA I strip say row[2], which I named sAr2 and which has values: sAr2 = [D, C, B, A] I also created sub arrays of columns, as listed below and furthermore, I created quadrants sub arrays. I would like to make a change on any of the sub arrays and have that change propagated simultaneously to the main array. For instance, say I set sAr2[1] = Y, I would like element mA[2,1] to change to Y from C. The same should happen if and when I change any of the sub arrays. The same should happen if and when I change the main array. Is this possible say in 1.9.1? or do I need some kind of GEM? Main Array: mA = [ [A, B, C, D], [B, A, C, D], [D, C, B, A], [C, A, D, B] ] Sub Arrays: sAr0 (sub array row 0 to row n, where n is 3 for this case) sAr0 = [A, B, C, D] sAr1 = [B, A, C, D] sAr2 = [D, C, B, A] sAr3 = [C, A, D, B] sAc0 (sub array column 0 to column n, where n is 3 for this case) sAc0 = [A, B, D, C] sAc1 = [B, A, C, A] sAc2 = [C, C, B, D] sAc3 = [D, D, A, B] Four “quadrants?” arrays as follows: qA1: [[A, B B, A]] qA3: [[B, D A, B]] Etc. Thank you ---
**Author:** ![rubina](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e47c2d/32.png) [@rubina](https://www.ruby-forum.com/u/rubina)\ **Post date:** [April 7, 2009, 3:37pm UTC](https://www.ruby-forum.com/t/array-question-how-dynamic-is-dynamic/164927/2 "2009-04-07T15:37:31Z")
On Tue, Apr 7, 2009 at 2:50 PM, Ruby S. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > For example, assume I have main array mA as listed below. > From mA I strip say row[2], which I named sAr2 and which has values: sAr2 = > [D, C, B, A] > I also created sub arrays of columns, as listed below and furthermore, I > created quadrants sub arrays. > > I would like to make a change on any of the sub arrays and have that change > propagated simultaneously to the main array. > For instance, say I set sAr2[1] = Y, I would like element mA[2,1] to change > to Y from C. First thing that came to mind is to add a level of indirection, so that the array doesn’t contain the actual values, but an object that contains the values, like so: irb(main):001:0\> O = Struct.new :value =\> O irb(main):008:0\> A = “A” =\> “A” irb(main):009:0\> B = “B” =\> “B” irb(main):010:0\> C = “C” =\> “C” irb(main):013:0\> myAr = [[O.new(A), O.new(B), O.new(C)],[O.new(B), O.new(A), O.new(C)],[O.new(C), O.new(B), O.new(A)]] =\> [[#, #, #], [#, #, #], [#, #, #]] irb(main):017:0\> first\_row = myAr[0] =\> [#, #, #] irb(main):018:0\> Y = “Y” =\> “Y” irb(main):019:0\> first\_row[2].value = Y =\> “Y” irb(main):020:0\> myAr =\> [[#, #, #], [#, #, #], [#, #, #]] So by changing the value of the object pointed to by first\_row[0], you are really changing the same object that is referenced in the original array. Don’t know if this is convenient for you or not. Probably someone will come up with a better idea. Hope this helps, Jesus. ---
**Author:** ![rubina](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e47c2d/32.png) [@rubina](https://www.ruby-forum.com/u/rubina)\ **Post date:** [April 7, 2009, 3:41pm UTC](https://www.ruby-forum.com/t/array-question-how-dynamic-is-dynamic/164927/3 "2009-04-07T15:41:02Z")
On Apr 7, 8:50 am, Ruby S. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > sAr0 (sub array row 0 to row n, where n is 3 for this case) > sAr0 = [A, B, C, D] > sAr1 = [B, A, C, D] > sAr2 = [D, C, B, A] > sAr3 = [C, A, D, B] I suggest you use the Matrix class (in the standard library). Though for the row case, you don’t need anything special: sAr0 = mA[0] = [A, B, C, D] sAr1 = mA[1] = [B, A, C, D] sAr2 = mA[2] = [D, C, B, A] sAr3 = mA[3] = [C, A, D, B] If you change sAr0, it will be reflected in mA[0]. – Mark. ---
**Author:** ![rubina](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e47c2d/32.png) [@rubina](https://www.ruby-forum.com/u/rubina)\ **Post date:** [April 7, 2009, 6:00pm UTC](https://www.ruby-forum.com/t/array-question-how-dynamic-is-dynamic/164927/4 "2009-04-07T18:00:43Z")
On 07.04.2009 15:38, Mark T. wrote: > > Sub Arrays: > > sAr0 (sub array row 0 to row n, where n is 3 for this case) > > sAr0 = [A, B, C, D] > > sAr1 = [B, A, C, D] > > sAr2 = [D, C, B, A] > > sAr3 = [C, A, D, B] > > I suggest you use the Matrix class (in the standard library). Are you sure this works? It seems, when I create a row Vector of the Matrix it is read only. At least []= is defined private. But I agree to the general advice to use a special class for this and not try to work with nested Arrays. That’s what OO is for. Defining a two dimensional matrix with Vector proxies isn’t too hard. Kind regards robert ---
**Author:** ![rubina](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e47c2d/32.png) [@rubina](https://www.ruby-forum.com/u/rubina)\ **Post date:** [April 9, 2009, 3:00pm UTC](https://www.ruby-forum.com/t/array-question-how-dynamic-is-dynamic/164927/5 "2009-04-09T15:00:40Z")
On Tue, Apr 7, 2009 at 11:59 AM, Robert K. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)wrote: > > > [C, A, D, B] > > > I suggest you use the Matrix class (in the standard library). > > ``` > robert > > ``` Thank you all for your input and suggestions!