python - pandas DataFrame diagonal

Question

What is an efficient way to get the diagonal of a square DataFrame. I would expect the result to be a Series with a MultiIndex with two levels, the first being the index of the DataFrame the second level being the columns of the DataFrame.

Setup

import pandas as pd
import numpy as np

np.random.seed([3, 1415])
df = pd.DataFrame(np.random.rand(3, 3) * 5,
                  columns = list('abc'),
                  index = list('ABC'),
                  dtype=np.int64
                 )

I want to see this:

print df.stack().loc[[('A', 'a'), ('B', 'b'), ('C', 'c')]]

A  a    2
B  b    2
C  c    3

Answer 1

If you don't mind using numpy you could use numpy.diag

pd.Series(np.diag(df), index=[df.index, df.columns])

A  a    2
B  b    2
C  c    3
dtype: int64