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digitalmars.D.learn - Transposing a static array

reply maik klein <maikklein googlemail.com> writes:
How would I transpose

float[3][2]

to

float[2][3]
Feb 19 2016
parent reply =?UTF-8?Q?Ali_=c3=87ehreli?= <acehreli yahoo.com> writes:
On 02/19/2016 06:00 PM, maik klein wrote:

 How would I transpose

 float[3][2]

 to

 float[2][3]




Because static arrays are not ranges, they must be used as slices with 
the help of []. The following code does the same thing in two different 
ways:

import std.stdio;
import std.range;
import std.algorithm;

void main() {
     float[3][2] arr = [ [1, 2, 3],
                         [4, 5, 6] ];

     // Method A
     {
         float[][] arr2;

         foreach (ref a; arr) {
             arr2 ~= a[];
         }

         writeln(arr2.transposed);
     }

     // Method B
     {
         auto r = arr[].map!((ref a) => a[]).array.transposed;
         writeln(r);
     }
}

Ali
Feb 19 2016
parent reply maik klein <maikklein googlemail.com> writes:
On Saturday, 20 February 2016 at 02:22:12 UTC, Ali Çehreli wrote:

 On 02/19/2016 06:00 PM, maik klein wrote:

 How would I transpose

 float[3][2]

 to

 float[2][3]




 Because static arrays are not ranges, they must be used as 
 slices with the help of []. The following code does the same 
 thing in two different ways:

 import std.stdio;
 import std.range;
 import std.algorithm;

 void main() {
     float[3][2] arr = [ [1, 2, 3],
                         [4, 5, 6] ];

     // Method A
     {
         float[][] arr2;

         foreach (ref a; arr) {
             arr2 ~= a[];
         }

         writeln(arr2.transposed);
     }

     // Method B
     {
         auto r = arr[].map!((ref a) => a[]).array.transposed;
         writeln(r);
     }
 }

 Ali


Your "Method B" is how I did it too but how do I convert it back 
to a static array of float[2][3]?
Feb 19 2016
next sibling parent reply cym13 <cpicard openmailbox.org> writes:
On Saturday, 20 February 2016 at 02:26:56 UTC, maik klein wrote:

 On Saturday, 20 February 2016 at 02:22:12 UTC, Ali Çehreli 
 wrote:

 On 02/19/2016 06:00 PM, maik klein wrote:

 How would I transpose

 float[3][2]

 to

 float[2][3]




 Because static arrays are not ranges, they must be used as 
 slices with the help of []. The following code does the same 
 thing in two different ways:

 import std.stdio;
 import std.range;
 import std.algorithm;

 void main() {
     float[3][2] arr = [ [1, 2, 3],
                         [4, 5, 6] ];

     // Method A
     {
         float[][] arr2;

         foreach (ref a; arr) {
             arr2 ~= a[];
         }

         writeln(arr2.transposed);
     }

     // Method B
     {
         auto r = arr[].map!((ref a) => a[]).array.transposed;
         writeln(r);
     }
 }

 Ali


 Your "Method B" is how I did it too but how do I convert it 
 back to a static array of float[2][3]?


I don't see the point of using transposed which gives a range out 
if you want to put it back into a float[2][3] right away, just do 
a double foreach:

     void main(string[] args) {
         float[3][2] src = [[1, 2, 3], [2, 3, 4]];

         float[2][3] dst;

         foreach (i ; 0..src.length)
             foreach (j ; 0..src[0].length)
                 dst[j][i] = src[i][j];

         assert(dst == [[1, 2], [2, 3], [3, 4]]);
     }
Feb 19 2016
parent maik klein <maikklein googlemail.com> writes:
On Saturday, 20 February 2016 at 03:02:11 UTC, cym13 wrote:

 On Saturday, 20 February 2016 at 02:26:56 UTC, maik klein wrote:

 On Saturday, 20 February 2016 at 02:22:12 UTC, Ali Çehreli 
 wrote:

 [...]


 Your "Method B" is how I did it too but how do I convert it 
 back to a static array of float[2][3]?


 I don't see the point of using transposed which gives a range 
 out if you want to put it back into a float[2][3] right away, 
 just do a double foreach:

     void main(string[] args) {
         float[3][2] src = [[1, 2, 3], [2, 3, 4]];

         float[2][3] dst;

         foreach (i ; 0..src.length)
             foreach (j ; 0..src[0].length)
                 dst[j][i] = src[i][j];

         assert(dst == [[1, 2], [2, 3], [3, 4]]);
     }


You are right. I restricted myself from using indices because I 
wanted to learn ranges but I think that working with matrices is 
actually much simpler by just using good old for loops.
Feb 20 2016
prev sibling parent =?UTF-8?Q?Ali_=c3=87ehreli?= <acehreli yahoo.com> writes:
On 02/19/2016 06:26 PM, maik klein wrote:

 On Saturday, 20 February 2016 at 02:22:12 UTC, Ali Çehreli wrote:

 On 02/19/2016 06:00 PM, maik klein wrote:

 How would I transpose

 float[3][2]

 to

 float[2][3]









         auto r = arr[].map!((ref a) => a[]).array.transposed;




There is a problem there. Adding the following line

     writeln(r.array);

causes an error:

core.exception.AssertError /usr/include/dmd/phobos/std/range
primitives.d(2207): 
Attempting to fetch the front of an empty array of float

Adding the following two lines does *not* preserve the range (first one 
does):

     writeln(r.save);
     writeln(r.save);

Did I not need (ref a) up there? I thought it would be a reference to a 
float[3] element.


         writeln(r);
     }
 }

 Ali


 Your "Method B" is how I did it too but how do I convert it back to a
 static array of float[2][3]?


I don't know. :D

Ali
Feb 19 2016