Indexing in operator() wrong for xview with xt::newaxis()?

I have a small problem with assigning to an xview that was created from an xtensor with xt::newaxis(). The code is given below, and also in a separate PR for review. I'm under the impression that the indexing is somehow incorrect. Here is the code sample:

    xt::xtensor<uint8_t, 2> aTensor = xt::zeros<uint8_t>({4, 3});
    auto aView = xt::view(aTensor, xt::newaxis(), xt::newaxis(), xt::newaxis(), xt::all(), xt::all());
    uint8_t vIndex = 0;
    // Counting only until (vRow < 3) here, otherwise we get an out-of-bounds exception:
    for (size_t vRow = 0; vRow < 3; ++vRow) {
        for (size_t vCol = 0; vCol < 3; ++vCol) {
            aView(size_t{0}, size_t{0}, size_t{0}, vRow, vCol) = vIndex;
            EXPECT_EQ(aTensor(vRow, vCol), vIndex);        ///< This finds the elements are *not* equal
            ++vIndex;
        }
    }

Similar issue here.

The pic is a xt::xarray<uint16_t>

auto&& patch = xt::view(pic, xt::range(i, i + tile_height), xt::range(j, j + tile_width));

The follow code is correct.

// Code1
for (uint k = 0; k < tile_height; ++k) {
    for (uint l = 0; l < tile_width; ++l) {
        patch.at(k, l) = payload.get();
    }
}

But these code is wrong

// Code2
for (uint k = 0; k < tile_height * tile_width; ++k) {
    patch(k) = payload.get();
}

For what its worth, here is what I could see in the debugger:

in xt::xview in operator() everything seems correct and indexes are checked correctly.
then the view seems to call the operator() of the underlying memory holding container (in my case a 2D xtensor)
- in this different-dimensional operator(), the indexes seem messed up. It looks like they would be in reverse order, or maybe some padding is missing or too much.

This would be nice to be fixed, esp. because its a "silent" error where the code actually seems to work but gives wrong results.

Kindly pinging this issue...

Kindly pinging this issue, that seems to perform wrong indexing (could be a bad bug?)

Fixed in #2896

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Indexing in operator() wrong for xview with xt::newaxis()? #2228

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Indexing in operator() wrong for xview with xt::newaxis()? #2228

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zYeoman commented on Nov 26, 2020

emmenlau commented on Nov 26, 2020

emmenlau commented on Jan 22, 2021

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Alex-PLACET commented on May 4, 2026

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