New issue 1278: Unable to filter a dataset using a derived field https://bitbucket.org/yt_analysis/yt/issues/1278/unable-to-filter-a-dataset-... Danielle Sponseller: When defining a particle filter, a derived field cannot be used to determine which particles to filter out. The example below shows a field defined to be equivalent to the "particle_position_x" field. When using "particle_position_x' in the filter definition, the filter works as expected, however when the derived field is used an error is returned saying that the field cannot be found. ``` #!python import yt import yt.units as units @yt.particle_filter(requires=["myField"], filtered_type='all') def small_x(pfilter, data): filter = data[(pfilter.filtered_type, "myField")] < 0 return filter snap = 'GadgetDiskGalaxy' ds = yt.load(snap, bounding_box = [[-8000, 8000], [-8000, 8000], [-8000, 8000]]) ds.add_particle_filter('small_x') def myField(field, data): return data["particle_position_x"] ds.add_field("myField", function=myField, units="kpc", particle_type = True) ds_disk_angular_momentum = yt.ParticlePlot(ds, ('small_x', 'particle_position_x'), ('small_x', 'particle_position_y'), ('small_x', 'myField'), width=(2000, 'kpc')) ds_disk_angular_momentum.save("Plot") ```