What are levels in a pandas DataFrame?

Question

I\'ve been reading through the documentation and many explanations and examples use levels as something taken for granted. Imho the docs lack a bit on a fundame

Answer 1

Usually a DataFrame has a 1D index and columns:

    x y
0   4 1
1   3 9

Here the index is [0, 1] and the columns are ['x', 'y']. But you can have multiple levels in either the index or the columns:

    x y
    a b c
0 7 4 1 3
  8 3 9 5

Here the columns' first level is ['x', 'y', 'y'] and the second level is ['a', 'b', 'c']. The index's first level is [0, 0] and the second level is [7, 8].