Python Pandas : group by in group by and average?

Question

I have a dataframe like this:

cluster  org      time
   1      a       8
   1      a       6
   2      h       34
   1      c       23
   2      d       74
   3      w       6

I would like to calculate the average of time per org per cluster.

Expected result:

cluster mean(time)
1       15 ((8+6)/2+23)/2
2       54   (74+34)/2
3       6

I do not know how to do it in Pandas, can anybody help?

Sorry are you wanting df.groupby(['org','cluster']).mean()? this isn't that meaningful for your dataset as opposed to this: df.groupby(['cluster','org']).mean() — EdChum
@EdChum thanks for your help, but I want is none of them. But the "average of average times per org". Please see the expected result (edited) — UserYmY

Zero Zero · Accepted Answer · 2015-05-19T14:37:03

If you want to first take mean on the combination of ['cluster', 'org'] and then take mean on cluster groups, you can use:

In [59]: (df.groupby(['cluster', 'org'], as_index=False).mean()
            .groupby('cluster')['time'].mean())
Out[59]:
cluster
1          15
2          54
3           6
Name: time, dtype: int64

If you want the mean of cluster groups only, then you can use:

In [58]: df.groupby(['cluster']).mean()
Out[58]:
              time
cluster
1        12.333333
2        54.000000
3         6.000000

You can also use groupby on ['cluster', 'org'] and then use mean():

In [57]: df.groupby(['cluster', 'org']).mean()
Out[57]:
               time
cluster org
1       a    438886
        c        23
2       d      9874
        h        34
3       w         6

Python Pandas : group by in group by and average?

2 Answers