python - Multi Index Sorting in Pandas

Question

I have a dataset with multi-index columns in a pandas df that I would like to sort by values in a specific column. I have tried using sortindex and sortlevel but haven't been able get the results I am looking for. My dataset looks like:

    Group1    Group2
    A B C     A B C
1   1 0 3     2 5 7
2   5 6 9     1 0 0
3   7 0 2     0 3 5 

I want to sort all data and the index by column C in Group 1 in descending order so my results look like:

    Group1    Group2
    A B C     A B C
 2  5 6 9     1 0 0
 1  1 0 3     2 5 7
 3  7 0 2     0 3 5 

Is it possible to do this sort with the structure that my data is in, or should I be swapping Group1 to the index side?

Answer 1

When sorting by a MultiIndex you need to contain the tuple describing the column inside a list*:

In [11]: df.sort_values([('Group1', 'C')], ascending=False)
Out[11]: 
  Group1       Group2      
       A  B  C      A  B  C
2      5  6  9      1  0  0
1      1  0  3      2  5  7
3      7  0  2      0  3  5

* so as not to confuse pandas into thinking you want to sort first by Group1 then by C.

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Note: Originally used .sort since deprecated then removed in 0.20, in favor of .sort_values.