Filtering multidimensional views in xtensor - c++

Question

I am trying to filter a 2D xtensor view with a simple condition. I found the xt::filter function, but when i use it, it only return the first column of the filtered view. I need the 2D filtered view. What is the best way to do it?
I could check the condition line by line, and get all the indexes myself, and the use xt::view to only show the needed lines, but i am hopig in a more sophisticated method using the xtensor toolset.
My current filter, which returns only one direction looks like this:
auto unfiltered = xt::view(...);
auto filtered = xt::filter(unfiltered, xt::view(unfiltered, xt::all(), 0) > tresh);
EDIT:
It is possible i was not completly clear. I need a 2D view where i kept only those lines, where the first element of the line is greater than the treshold.

Answer 1

xt::view(unfiltered, xt::all(), 0)
is creating a view that only contains the first column of unfiltered. The following should do what you expect:
auto unfiltered = xt::view(...);
auto filtered = xt::filter(unfiltered, unfiltered > tresh);
EDIT: sorry for the misunderstanding, here is an update following OP remark:
The condition is not broadcast to the shape of the expression to filter, a workaround for now is:
auto unfiltered = xt::view(...);
auto filtered = xt::filter(unfiltered,
xt::broadcast(xt::view(unfiltered, xt::all(), 0, xt::newaxis()),
unfiltered.shape()) > tresh);
I'll open an issue for this.
Also notice that filter returns a 1D expression (because the elements satisfying a condition may be scattered in the original expression), you need to reshape it to get a 2D expression.