Hi José, 

Unfortunately the old halo finders (HOP/FOF) don't accept a particle type keyword argument at the moment. 

There's a work in progress PR that implements a new version of FOF that should allow you to specify a particle

type, it just hasn't been merged into mainline yt because it's not completely tested. It's available here 

(https://bitbucket.org/yt_analysis/yt/pull-requests/1618/wip-hybrid-rockstar/) if you wanted to test it out, and

you could run the new version of FOF as follows:

```
from yt.analysis_modules.halo_analysis.api import HaloCatalog

...

hc = HaloCatalog(data_ds=ds, finder_method='yt_fof',

                             finder_kwargs={'particle_type':'my_particle_type'})
hc.create()

```

Sorry thats not completely helpful, but hopefully we should have this fully implemented soon!

-Hilary

On Thu, Sep 3, 2015 at 10:45 AM, José Utreras <jutreras@das.uchile.cl> wrote:

Hi Nathan!

I thought in using the filters but I don't see how to pass this information to the group-finder methods before the groups are identified.

2015-09-02 15:49 GMT-04:00 Nathan Goldbaum <nathan12343@gmail.com>:

I'm not sure how it interacts with the halo finding / FOF machinery, but you may be interested in this docs page on particle filters:

http://yt-project.org/docs/dev/analyzing/filtering.html#filtering-particle-fields

On Wed, Sep 2, 2015 at 2:43 PM, José Utreras <jutreras@das.uchile.cl> wrote:

Hi everyone

I'm working with Enzo and I'm trying to identify groups of stars particles. Now I wanted to create groups but only of young stars. I thought using HOP but I don't see how to filter particles before crating the groups.

Thanks!

Jose

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--

Hilary Egan

Astrophysical and Planetary Science Department

University of Colorado Boulder

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