The representation above is redundant, because to encode three values you need two indicator columns. In general, one needs d - 1 columns for d values. This is not a big deal, but apparently some methods will complain about collinearity. The solution is to drop one of the columns. It won’t result in information loss, because in the redundant scheme with d columns one of the indicators must be non-zero, so if two out of three are zeros then the third must be 1. And if one among the two is positive than the third must be zero.
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