I have a following sample data frame. How can I create a group id of column and b and to obtain column c? a b c 1 1 1 1 1 1 1 1 1 1 2 2 1 2 2 1 2 2 1 3 3 1 3 3 1 3 3 2 1 4 2 1 4 2 1 4 2 2 5 2 2 5 2 2 5 2 2 5 [[alternative HTML version deleted]]
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