Pandas MultiIndex DataFrame

Question

I have an array:

w = np.array([1,  2,  3])

and I need to create a Dataframe with a MultiIndex looking like this:

df=  0  1  2
0 0  1  1  1
  1  1  1  1
  2  1  1  1
1 0  2  2  2
  1  2  2  2
  2  2  2  2
2 0  3  3  3
  1  3  3  3
  2  3  3  3

How can i assign the values of my array to the correct positions in the DataFrame?

The input is only w or do you also have a preexisting single-indexed dataframe? — mozway
– mozway, Commented Apr 10, 2022 at 18:16

mozway · Accepted Answer · 2022-04-10 18:21:33Z

1

The exact logic is unclear, by assuming w is the only input and you want to broadcast it as index(0,1) and columns:

w = np.array([1,  2,  3])

N = len(w)
df = pd.DataFrame(np.repeat(w, N**2).reshape((-1,N)),
                  index=pd.MultiIndex.from_product([np.arange(N)]*2)
                  )

output:

     0  1  2
0 0  1  1  1
  1  1  1  1
  2  1  1  1
1 0  2  2  2
  1  2  2  2
  2  2  2  2
2 0  3  3  3
  1  3  3  3
  2  3  3  3

answered Apr 10, 2022 at 18:21

mozway

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2 Comments

cobra Over a year ago

this is helping and getting me foreward! I need to find good sources to learn how to transform DataFrames, have you any suggestions for me?

mozway Over a year ago

Try, fail, read the docs, search stackoverflow, try again, succeed ;)

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