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# Specifying Prior Probabilities

Is there a way to specify prior probabilities in Rapid Miner? For example let's say I have a dataset that has 80% of one class and 20% of another class. A subset is created that has 50% of both classes. I would like to be able to specify that the prior probabilities were 80% and 20%.

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## Answers

849MavenYou could do this by filtering and counting using data macros, but a quick and sneaky fix sometimes has its place, like this... Good weekend to all!

157MavenKeith

849MavenHave you not heard? Backwards is the new forwards! Perhaps I should have been more explicit; we can use the fact that we know the number of classes and the 'equal weight' number to keep track of the original distribution. In the binominal case we simply divide 0.5 by the weight to produce the count, like this...