Hi,
assumed, I need the size of a dynamic array for further processing, which is unknown at compile time. Below are my example, which doesn't work and two alternatives.

Alternative1: may create large rowT-arrays depending on original array size.
Alternative2: overrides rowT after exiting the inner loop (which may be costly?)

How could I implement something like the first approach?

Thanks!

// Not working example of transposing a matrix
double[][] transp(double[][] array)
{
  double[][] arrayT;
  double[array[0].length] rowT;
  foreach(col; 0..array[0].length)
  {
    foreach(row; array)
    {
      rowT[col]= row[col];
    }
    arrayT ~= rowT;
  }
  return arrayT;
}

// Alternative1
  double[][] arrayT;
  double[] rowT;
  foreach(col; 0..array[0].length)
  {
    foreach(row; array)
    {
      rowT ~= row[col];
    }
    arrayT ~= rowT[$-6..$];
  }

// Alternative2
  double[][] arrayT;
  foreach(col; 0..array[0].length)
  {
    double[] rowT;
    foreach(row; array)
    {
      rowT ~= row[col];
    }
    arrayT ~= rowT;
  }

On Sunday, 1 October 2017 at 10:07:40 UTC, thorstein wrote:
> Hi,
> assumed, I need the size of a dynamic array for further processing, which is unknown at compile time. Below are my example, which doesn't work and two alternatives.
>
> [...]

They are not alternatives. They are the only way of doing things.

> They are not alternatives. They are the only way of doing things.

Yes, sounds logic - static arrays require a size before compilation.
However, I tried another variation with a totally unexpected result:

double[][] transp3(double[][] array)
{

  double[][] arrayT;
  double[] rowT;
  // initialize rowT
  foreach(i; 0..array.length)
  {
    rowT ~= 0;
  }

  foreach(col; 0..array[0].length)
  {
    foreach(row; 0..array.length)
    {
      rowT[row] = array[row][col];
    }
    arrayT ~= rowT;

    writeln("rowT: ",rowT);
    writeln("arrayT: ", arrayT);
  }
    return arrayT;
}

Assuming my original array to be:
  array =
    [
      [ 4,  3,   1,   5,  2],
      [19, 34,  23, 100, 59],
      [62,  1,   4,   0, 76],
      [23,  6, 989,  98,  1],
      [ 5, 87,  45,  62,  9],
      [ 5, 87,  45,  62,  9]
    ];

...then the printed result is unexpectedly wrong. The transposed columns (rowT) are correct, but arrayT ~= rowT doesn't only append rowT to arrayT. It overrides also the previous rows with the new transposed column:
rowT: [4, 19, 62, 23, 5, 5]
arrayT: [[4, 19, 62, 23, 5, 5]]
rowT: [3, 34, 1, 6, 87, 87]
arrayT: [[3, 34, 1, 6, 87, 87], [3, 34, 1, 6, 87, 87]]
etc...

Why is that????

Thanks!

On Sunday, 1 October 2017 at 13:53:57 UTC, thorstein wrote:

>
> Why is that????
>
> Thanks!

Guyes, I obviously made a mistake. Forget my post!

> Guyes, I obviously made a mistake. Forget my post!

Sorry, I'm still really confused with the results from my function:

double[][] transp(double[][] array)
{

  double[][] arrayT;
  double[] rowT;
  // initialize rowT
  foreach(i; 0..array.length)
  {
    rowT ~= 0;
  }

  foreach(col; 0..array[0].length-3)
  {
    foreach(row; 0..array.length)
    {
      rowT[row] = array[row][col];
    }
    writeln("rowT 1: ",rowT);
    writeln("arrayT 1: ", arrayT);
    arrayT ~= rowT;
    writeln("rowT 2: ",rowT);
    writeln("arrayT 2: ", arrayT,"\n");
  }
    return arrayT;
}

Again, assuming my original array to be:
  array =
    [
      [ 4,  3,   1,   5,  2],
      [19, 34,  23, 100, 59],
      [62,  1,   4,   0, 76],
      [23,  6, 989,  98,  1],
      [ 5, 87,  45,  62,  9],
      [ 5, 87,  45,  62,  9]
    ];

... the results are strange. Before the appending (arrayT ~= rowT;) happens for the second column of array arrayT was miraculous modified:

rowT 1: [4, 19, 62, 23, 5, 5]
arrayT 1: []
rowT 2: [4, 19, 62, 23, 5, 5]
arrayT 2: [[4, 19, 62, 23, 5, 5]]

rowT 1: [3, 34, 1, 6, 87, 87]
arrayT 1: [[3, 34, 1, 6, 87, 87]]
rowT 2: [3, 34, 1, 6, 87, 87]
arrayT 2: [[3, 34, 1, 6, 87, 87], [3, 34, 1, 6, 87, 87]]

etc...

Is there any linkage between rowT and arrayT????

Thanks again!

On Sunday, 1 October 2017 at 14:23:54 UTC, thorstein wrote:
>> [...]
>
> Sorry, I'm still really confused with the results from my function:
>
> [...]

Replace
arrayT ~= rowT;
with
arrayT ~= rowT.dup;

Also, you may want to look into ndslice package [1].
[1] https://github.com/libmir/mir-algorith

Best regards,
Ilya Yaroshenko

> Replace
> arrayT ~= rowT;
> with
> arrayT ~= rowT.dup;
>
> Also, you may want to look into ndslice package [1].
> [1] https://github.com/libmir/mir-algorithm
>
> Best regards,
> Ilya Yaroshenko

Works! Thanks Ilya. I'll take a look on the difference. Also soon will get bit familiar with the mir-algorithm...

Best, Torsten