pandas: convert index type in multiindex dataframe

问题:

Hi have a multiindex dataframe:

tuples = [('YTA_Q3', 1), ('YTA_Q3', 2), ('YTA_Q3', 3), ('YTA_Q3', 4), ('YTA_Q3', 99), ('YTA_Q3', 96)]
# Index
index = pd.MultiIndex.from_tuples(tuples, names=['Questions', 'Values'])
# Columns
columns = pd.MultiIndex.from_tuples([('YTA_Q3', '@')], names=['Questions', 'Values'])
# Data
data = [29.014949,5.0260590000000001,
  6.6269119999999999,
  1.3565260000000001,
  41.632221999999999,
  21.279499999999999]

df1 = pd.DataFrame(data=data, index=index, columns=columns)

How do I convert the inner values of the df's index to str?

My attempt:

df1.index.astype(str) 

returns a TypeError

回答1:

IIUC you need the last level of Multiindex. You could access it with levels:

df1.index.levels[-1].astype(str)

In [584]: df1.index.levels[-1].astype(str)
Out[584]: Index(['1', '2', '3', '4', '96', '99'], dtype='object', name='Values')

EDIT

You could set your inner level with set_levels method of multiIndex:

idx = df1.index
df1.index = df1.index.set_levels([idx.levels[:-1], idx.levels[-1].astype(str)])

回答2:

I find the current pandas implementation a bit cumbersome, so I use this:

df1.index = pd.MultiIndex.from_tuples([(ix[0], str(ix[1])) for ix in df1.index.tolist()])