I have a scene of many objects using several materials. Some of the objects use multiple materials applied with primitive groups.
I would like to render out a shadow matte/pass for just one of the materials and have that be the only thing visible on the image. All of the other materials/objects need to be transparent or held out so that I only end up with a shadow pass on that one specific primitive group.

Is this possible? I can easily render out the shadow passes for the entire scene but how would one go about isolating it to a specific material group?

Maybe use Phantom
you can add the parameter to your geo, too.
see http://www.sidefx.com/docs/houdini/network/patterns.html [www.sidefx.com]
if you like to match objects by given names

Oooh I gave up too easily…
simple solution was to just to merge and split geometry among two object nodes using my groups for materials.
One with matte shading the other with a shadow matte material.

>>
Maybe use Phantom
you can add the parameter to your geo, too.
<<

thank you Matthias. That is a great tip and looks like it would be very useful especially if I am using a naming convention for my nodes. wow Houdini is always amazing me with the possibilities for doing things