PROC PLS is designed for partial least squares regression, which seeks linear combinations of predictor variables that explain as much variation as possible in the response variables. In PROC PLS, the response (Y) variables must be numeric. Therefore, when predictors are binary or categorical, they can be specified in the CLASS statement, but they cannot be used as response variables in the MODEL statement (otherwise an error is returned). As a result, you cannot make the X-variables identical to the Y-variables when the inputs are binary or categorical specified in CLASS statement.
Binary or categorical variables can be replaced by dummy variables as responses in PROC PLS. And then you use the same dummy variables on both sides of the PLS equation. So it can be done. Whether or not it is a good idea, I can't say.
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