# Working with alternative halo and particle catalogs¶

This section of the documentation describes how you can use Halotools with simulations besides the pre-processed snapshots that come standard with the package.

## Reducing a new Rockstar catalog¶

The RockstarHlistReader class allows you to read the ASCII output of the Rockstar halo-finder, apply row- and column-wise cuts of your choosing, and store the resulting catalog in the Halotools cache as a fast-loading hf5 file. If this is your use-case, see the Instructions for Reducing and Caching a Rockstar Catalog section of the documentation.

If you want to reduce your own Rockstar catalog with Halotools but do not want to store the catalog in cache, you should instead use the stand-alone TabularAsciiReader class.

## Using alternative catalogs¶

The full functionality of Halotools is available for use with halos in any N-body simulation identified with any halo-finder, and use of the Halotools caching system is optional in every respect. For more information about how to work with simulation data not provided by Halotools, see Instructions for Working with an Alternative Halo Catalog.

## Using your own collection of dark matter particles¶

Some features in Halotools requires use of a catalog of a random sample of dark matter particles from the same snapshot as the halo catalog. Most of the Halotools-provided halo catalogs are accompanied by a corresponding particle catalog, but you may prefer to provide your own, or you may wish to use these features with alternative simulation data. See the Instructions for Working with Alternative Particle Data section of the documentation for how to put your collection of particles into a standard form and optionally store the particle data in your cache.