I am working on a binary classification task where one of the input variables takes values in {A, B, C}. A lot of classifiers only take numerical attributes as inputs so I was wondering what the best way to do this is. If I just map them to integers like A:1, B:2, C:3, I am worried that this would mean that A is more similar to B and less similar to C (because |1-2|=1 and |1-3|=2) but that is not necessarily true. So won't this method introduce some sort of bias?