What would be the best way to find all voxels in a volume which satisfy certain conditions and copy the in a new volume / or delete all voxels which do not satisfy the conditions. example of condition would be density > 0.1 && density < 0.5 for example or in my case it would be density == 0.2 for example.

At the moment i use python and numpy but I thought there should be a native houdini way…

A volumeVOP with volume sample vop inside would work nicely for that task.

That is if you by delete mean set value to 0.