[yt-dev] Issue #1172: ParticlePlot does not work on filtered particles (yt_analysis/yt)

[Yi-Hao Chen]

New issue 1172: ParticlePlot does not work on filtered particles
https://bitbucket.org/yt_analysis/yt/issues/1172/particleplot-does-not-work-on-filtered

Yi-Hao Chen:

If ParticlePlot is fed with a filtered particle field, it will read the filtered field and try to apply the filter again. I am not sure where the bug is, but at least it affects the ParticlePlot. The bug can be reproduced by the following script derived from the cookbook.

```
import yt
from yt.data_objects.particle_filters import add_particle_filter

def formed_star(pfilter, data):
    filter = data["all", "creation_time"] > 0
    return filter

add_particle_filter("formed_star", function=formed_star, filtered_type='all',
                    requires=["creation_time"])

ds = yt.load('IsolatedGalaxy/galaxy0030/galaxy0030')
ds.add_particle_filter('formed_star')

p = yt.ParticlePlot(ds, 'particle_position_y', 'particle_position_z', ('formed_star', 'particle_mass'))
p.show()
```