The filter condition is not broadcasted to match the shape of the expression we want to filter. FOr instance, the following code returns all the elements of the first column bigger than the treshold instead of returning all the ellements of lines whose first element is bigger than the treshold:

xarray<int> a = { { 0, 1, 2, 3 },
                  { 4, 5, 6, 7 },
                  { 8, 9, 10, 11 } };
auto filter = xt::filter(a, xt::view(a, xt::all(), 0) > 4);
std::cout << filter << std:endl;

Result:

{ 8 }

Expected result:

{8, 9, 10, 11}