moin Eric, moin list,
There may be a more elegant way to do this, but I'd use which($mask) to
feed dice_axis() of $target. Using your $mask example above:
pdl2> $mask = pdl([0,0,1,0,1,1,1,0,1,0])->slice("*1,")
pdl2> p $selected = $target->dice_axis(1, $mask->flat->which)
[
[10 11 12 13 14]
[20 21 22 23 24]
[25 26 27 28 29]
[30 31 32 33 34]
[40 41 42 43 44]
]
... now you should be able to alter $selected and have the data propagate
auto-magically back to $target:
pdl2> $selected **= 2
pdl2> p $target
[
[ 0 1 2 3 4]
[ 5 6 7 8 9]
[ 100 121 144 169 196]
[ 15 16 17 18 19]
[ 400 441 484 529 576]
[ 625 676 729 784 841]
[ 900 961 1024 1089 1156]
[ 35 36 37 38 39]
[1600 1681 1764 1849 1936]
[ 45 46 47 48 49]
]
Hope it helps,
Bryan
On Wed, Aug 9, 2023 at 9:30 AM Eric Wheeler <[email protected]> wrote:
> Hello all!
>
> I would like to get a diced/sliced/indexed piddle that is derived from a
> larger matrix based on rows indicated by a mask.
>
> For example, lets say I have a mask and I want to dice a matrix's rows
> where the mask has a value of 1 (in any location):
>
> pdl> p $mask = random(10)->transpose > 0.5
>
> [
> [0]
> [0]
> [1]
> [0]
> [1]
> [1]
> [1]
> [0]
> [1]
> [0]
> ]
>
> and lets say that this is the origin matrix I want to dice:
>
> pdl> p $target = sequence(5, 10)
>
> [
> [ 0 1 2 3 4]
> [ 5 6 7 8 9]
> [10 11 12 13 14]
> [15 16 17 18 19]
> [20 21 22 23 24]
> [25 26 27 28 29]
> [30 31 32 33 34]
> [35 36 37 38 39]
> [40 41 42 43 44]
> [45 46 47 48 49]
> ]
>
> I would like to have a result that has only the rows where the mask is
> marked with a 1, like this:
>
> $result = filter_somehow_from($target by $mask);
> [
> [30 31 32 33 34]
> [35 36 37 38 39]
> [40 41 42 43 44]
> [45 46 47 48 49]
> ]
>
> so I can modify the result in-place, like square it:
>
> $result **= 2;
>
> [ 900 961 1024 1089 1156]
> [1225 1296 1369 1444 1521]
> [1600 1681 1764 1849 1936]
> [2025 2116 2209 2304 2401]
>
> so the `**= 2` will modify to the original matrix:
>
> [
> [ 0 1 2 3 4]
> [ 5 6 7 8 9]
> [10 11 12 13 14]
> [15 16 17 18 19]
> [20 21 22 23 24]
> [25 26 27 28 29]
> [ 900 961 1024 1089 1156]
> [1225 1296 1369 1444 1521]
> [1600 1681 1764 1849 1936]
> [2025 2116 2209 2304 2401]
> ]
>
>
> I know I could do something with ->slice to modify in-place, but ':,6:9'
> is not $mask:
>
> pdl> p $target->slice(':,6:9') **= 2
>
> [
> [ 900 961 1024 1089 1156]
> [1225 1296 1369 1444 1521]
> [1600 1681 1764 1849 1936]
> [2025 2116 2209 2304 2401]
> ]
>
> pdl> p $target
>
> [
> [ 0 1 2 3 4]
> [ 5 6 7 8 9]
> [ 10 11 12 13 14]
> [ 15 16 17 18 19]
> [ 20 21 22 23 24]
> [ 25 26 27 28 29]
> [ 900 961 1024 1089 1156]
> [1225 1296 1369 1444 1521]
> [1600 1681 1764 1849 1936]
> [2025 2116 2209 2304 2401]
> ]
>
> So $mask defines the rows I need to modify, and $mask could have 1's in
> any location, and those are the locations I need to twiddle.
>
> Ideas?
>
> Thanks for your help!
>
> --
> Eric Wheeler
>
>
> _______________________________________________
> pdl-general mailing list
> [email protected]
> https://lists.sourceforge.net/lists/listinfo/pdl-general
>
--
Bryan Jurish "There is *always* one more bug."
[email protected] -Lubarsky's Law of Cybernetic Entomology
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