title: Get log(n, 2) features after dummy encoding
body: <p>During the dummy encoding (for example OneHotEncoder) we can drop first feature (with param: drop='first'). It helps when we have 3 features. It works because it's enough to have 2 cells to encoding 3 features like: (0, 0), (0, 1), (1, 0); also for 4 features: (0, 0), (0, 1), (1, 0), (1, 1). So I noticed that to encode n-categories it's enough to have math.ceil(log(n, 2)) features. But I can't find function (in sklearn/pandas) that allows to do this. I ask your help.</p>