I am currently working on a sprite tool for crowds and the client said theres far to many people who are wearing yellow shirts.So somehow I needed to bias the amount of players in my loops of frames more towards the guys with plain shirts.
With a great deal of help from eetu I have got a scene here showing how you can bias a particles ID . I have added an add attribute VOP so the attribute LOOPID can be used elsewhere inside Houdini. To see the scene in action, go to the details view , look at bias_loopid , then move the bias value slider on the vop sop to see the results.

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