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digitalmars.D.learn - select all rows (resp. columns) out of matrix

reply "seany" <seany uni-bonn.de> writes:
How do I access All rows (resp. columns ) of a Matrix / 
multidimensional array?

In scilab, you write array_var(:,row_index), colon meaning all 
columns, at that particular row given by row index will be 
selected.

can you, forexample, in D, write, array_var[0][] to select all 
elements (columns, in this case i believe?) of array_var[0] ?
Nov 14 2013
parent reply "TheFlyingFiddle" <theflyingfiddle gmail.com> writes:
On Thursday, 14 November 2013 at 22:06:28 UTC, seany wrote:

 How do I access All rows (resp. columns ) of a Matrix / 
 multidimensional array?

 In scilab, you write array_var(:,row_index), colon meaning all 
 columns, at that particular row given by row index will be 
 selected.

 can you, forexample, in D, write, array_var[0][] to select all 
 elements (columns, in this case i believe?) of array_var[0] ?


unittest
{
   int[][] matrix = new int[][](n,m);

   //Getting a collumn is simple.
   int[] collumn0 = matrix[0];

   //Getting a row is trickier
   int[] row0;

   //Loop over all collumns
   foreach(i; matrix) {
     row0 ~= matrix[i][0];
   }
}
Nov 14 2013
next sibling parent "TheFlyingFiddle" <theflyingfiddle gmail.com> writes:
On Thursday, 14 November 2013 at 22:18:44 UTC, TheFlyingFiddle 
wrote:

 unittest
 {
   int[][] matrix = new int[][](n,m);

   //Getting a collumn is simple.
   int[] collumn0 = matrix[0];

   //Getting a row is trickier
   int[] row0;

   //Loop over all collumns
   foreach(i; matrix) {
     row0 ~= matrix[i][0];
   }
 }


Sry the way you get rows is wrong.
It should be

int[] row0;
foreach(collumn; matrix)
     row0 ~= collumn[0];

and not


   int[] row0;

   //Loop over all collumns
   foreach(i; matrix) {
     row0 ~= matrix[i][0];
   }
Nov 14 2013
prev sibling parent reply =?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:
On 11/14/2013 02:18 PM, TheFlyingFiddle wrote:

 On Thursday, 14 November 2013 at 22:06:28 UTC, seany wrote:

 How do I access All rows (resp. columns ) of a Matrix /
 multidimensional array?

 In scilab, you write array_var(:,row_index), colon meaning all
 columns, at that particular row given by row index will be selected.

 can you, forexample, in D, write, array_var[0][] to select all
 elements (columns, in this case i believe?) of array_var[0] ?


 unittest
 {
    int[][] matrix = new int[][](n,m);

    //Getting a collumn is simple.
    int[] collumn0 = matrix[0];

    //Getting a row is trickier
    int[] row0;

    //Loop over all collumns
    foreach(i; matrix) {
      row0 ~= matrix[i][0];
    }
 }


transversal() is useful too: :)

   http://dlang.org/phobos/std_range.html#transversal

Ali
Nov 14 2013
next sibling parent "TheFlyingFiddle" <theflyingfiddle gmail.com> writes:
On Thursday, 14 November 2013 at 22:26:03 UTC, Ali Çehreli wrote:

 transversal() is useful too: :)

   http://dlang.org/phobos/std_range.html#transversal

 Ali


Did not know about this one. Thanks for pointing it out :D
Nov 14 2013
prev sibling parent reply "bearophile" <bearophileHUGS lycos.com> writes:
Ali Çehreli:


 transversal() is useful too: :)

   http://dlang.org/phobos/std_range.html#transversal


transversal() is sometimes useful, but if you need a significant 
amount of matrix processing, slicing and dicing matrices all the 
time in scientific code, then probably it's better to use a 
custom matrix library for D. Eventually one "winner" of such 
libraries should come out for D (as NumPy is in Python world). 
But to implement such libraries D should improve its management 
of "$" and "..." more for user-defined types.

Bye,
bearophile
Nov 14 2013
parent "H. S. Teoh" <hsteoh quickfur.ath.cx> writes:
On Fri, Nov 15, 2013 at 12:13:11AM +0100, bearophile wrote:

 Ali Çehreli:
 

transversal() is useful too: :)

  http://dlang.org/phobos/std_range.html#transversal


 
 transversal() is sometimes useful, but if you need a significant
 amount of matrix processing, slicing and dicing matrices all the
 time in scientific code, then probably it's better to use a custom
 matrix library for D. Eventually one "winner" of such libraries
 should come out for D (as NumPy is in Python world). But to
 implement such libraries D should improve its management of "$" and
 "..." more for user-defined types.


[...]

'$' already works for multidimensional arrays, you just have to
implement opDollar appropriately.

Slicing syntax isn't, though. Kenji has a pull for it, but it hasn't
been merged yet for whatever reason.


T

-- 
Once bitten, twice cry...
Nov 14 2013