how to get the id of primitive according to its color?
for example: how can i get the id of primitive (or point ) which variable Cd1>.5?
thanks

First off, welcome to the forums!

Your question is a little bit misleading… For example, primitives and points don't have an ID attribute by default (only particles do). There is however, a point/primitve number each one gets.

Secondly, what happens if 200 points/primitives in your scene have a $CR > .1 ? Which point/primitive number do you want it to return?

Perhaps we can be of more help if you explain what this is for.

On a side note, there is a poppointid expression that might be of use to you if this is for particles.

you can use the Group SOP…..

Thanks for the reply!!
I just want to select all the primitives or points which have certain indentical attribute, such as color, normal …
I use a Group SOP, and want to use a expression to select I want.
I dont konw which expression/SOP can doing this..

thanks again.

oh~~~ I get the answer
it is need a attribute create SOP to get variable, and then used in expression..

If you were grouping by color like in your first example, the variables you don't need an attribute create sop to create those custom variable mappings (so you can type $MY_VAR), Houdini already gives you those: $CR, $CG, and $CG for Red, Green, and Blue respectively