Hi

I am wondering if it is possible to assign a vector to a row of a matrix?

============ main.d ==========
import mir.ndslice;

void main() {

  auto matrix = slice!double(3, 4);
  matrix[] = 0;
  matrix.diagonal[] = 1;

  auto row = matrix[0];
  row[3] = 4;
  assert(matrix[0, 3] == 4);

  // assign it to rows of a matrix?
  auto vector = sliced!(double)([10, 11, 12, 13]);

  // ??? Here I would like to assign the vector to the last (but it is not working)
  // matrix[2] = vector;
}
============

So I am wondering what the correct way is to do such an assignment without looping?

On Saturday, 15 December 2018 at 19:04:37 UTC, David wrote:
> Hi
>
> I am wondering if it is possible to assign a vector to a row of a matrix?
>
> ============ main.d ==========
> import mir.ndslice;
>
> void main() {
>
>   auto matrix = slice!double(3, 4);
>   matrix[] = 0;
>   matrix.diagonal[] = 1;
>
>   auto row = matrix[0];
>   row[3] = 4;
>   assert(matrix[0, 3] == 4);
>
>   // assign it to rows of a matrix?
>   auto vector = sliced!(double)([10, 11, 12, 13]);
>
>   // ??? Here I would like to assign the vector to the last (but it is not working)
>   // matrix[2] = vector;
> }
> ============
>
> So I am wondering what the correct way is to do such an assignment without looping?

matrix[2][] = vector;

Or

matrix[2,0..$] = vector;

On Wednesday, 26 December 2018 at 18:59:25 UTC, 9il wrote:
> On Saturday, 15 December 2018 at 19:04:37 UTC, David wrote:
>> Hi
>>
>> I am wondering if it is possible to assign a vector to a row of a matrix?
>>
>> ============ main.d ==========
>> import mir.ndslice;
>>
>> void main() {
>>
>>   auto matrix = slice!double(3, 4);
>>   matrix[] = 0;
>>   matrix.diagonal[] = 1;
>>
>>   auto row = matrix[0];
>>   row[3] = 4;
>>   assert(matrix[0, 3] == 4);
>>
>>   // assign it to rows of a matrix?
>>   auto vector = sliced!(double)([10, 11, 12, 13]);
>>
>>   // ??? Here I would like to assign the vector to the last (but it is not working)
>>   // matrix[2] = vector;
>> }
>> ============
>>
>> So I am wondering what the correct way is to do such an assignment without looping?
>
> matrix[2][] = vector;
>
> Or
>
> matrix[2,0..$] = vector;

great many thanks!! Is there any logic why getting a row works by

auto row = matrix[0];

but assigning to a row works (only) by the two variant you posted?

On Thursday, 27 December 2018 at 21:17:48 UTC, David wrote:
> On Wednesday, 26 December 2018 at 18:59:25 UTC, 9il wrote:
>> On Saturday, 15 December 2018 at 19:04:37 UTC, David wrote:
>>> Hi
>>>
>>> I am wondering if it is possible to assign a vector to a row of a matrix?
>>>
>>> ============ main.d ==========
>>> import mir.ndslice;
>>>
>>> void main() {
>>>
>>>   auto matrix = slice!double(3, 4);
>>>   matrix[] = 0;
>>>   matrix.diagonal[] = 1;
>>>
>>>   auto row = matrix[0];
>>>   row[3] = 4;
>>>   assert(matrix[0, 3] == 4);
>>>
>>>   // assign it to rows of a matrix?
>>>   auto vector = sliced!(double)([10, 11, 12, 13]);
>>>
>>>   // ??? Here I would like to assign the vector to the last (but it is not working)
>>>   // matrix[2] = vector;
>>> }
>>> ============
>>>
>>> So I am wondering what the correct way is to do such an assignment without looping?
>>
>> matrix[2][] = vector;
>>
>> Or
>>
>> matrix[2,0..$] = vector;
>
> great many thanks!! Is there any logic why getting a row works by
>
> auto row = matrix[0];
>
> but assigning to a row works (only) by the two variant you posted?

This case gets a slice of a row, it does not copy the data. So row[i] is matrix[0, i], the same number in the RAM.

auto row = matrix[0];

This case gets a slice of a row, it does not copy the data.

If you wish to copy data you need to use a slice on the right side:

row[] = matrix[0];

or

auto row = matrix[0].slice; // 'slice' allocates new data

For columns:

col[] = matrix[0 .. $, 0];

On Friday, 28 December 2018 at 08:09:09 UTC, 9il wrote:
> On Thursday, 27 December 2018 at 21:17:48 UTC, David wrote:
>> On Wednesday, 26 December 2018 at 18:59:25 UTC, 9il wrote:
>>> On Saturday, 15 December 2018 at 19:04:37 UTC, David wrote:
>>>> [...]
>>>
>>> matrix[2][] = vector;
>>>
>>> Or
>>>
>>> matrix[2,0..$] = vector;
>>
>> great many thanks!! Is there any logic why getting a row works by
>>
>> auto row = matrix[0];
>>
>> but assigning to a row works (only) by the two variant you posted?
>
> This case gets a slice of a row, it does not copy the data. So row[i] is matrix[0, i], the same number in the RAM.
>
> auto row = matrix[0];
>
> This case gets a slice of a row, it does not copy the data.
>
> If you wish to copy data you need to use a slice on the right side:
>

EDIT: a slice on the LEFT side

On Friday, 28 December 2018 at 08:11:37 UTC, 9il wrote:
> On Friday, 28 December 2018 at 08:09:09 UTC, 9il wrote:
>> On Thursday, 27 December 2018 at 21:17:48 UTC, David wrote:
>>> On Wednesday, 26 December 2018 at 18:59:25 UTC, 9il wrote:
>>>> [...]
>>>
>>> great many thanks!! Is there any logic why getting a row works by
>>>
>>> auto row = matrix[0];
>>>
>>> but assigning to a row works (only) by the two variant you posted?
>>
>> This case gets a slice of a row, it does not copy the data. So row[i] is matrix[0, i], the same number in the RAM.
>>
>> auto row = matrix[0];
>>
>> This case gets a slice of a row, it does not copy the data.
>>
>> If you wish to copy data you need to use a slice on the right side:
>>
>
> EDIT: a slice on the LEFT side

Many thanks for this background!!