Python Pandas : group by in group by and average?

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?

Answers:

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Method 1

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

Method 2

I would simply do this, which literally follows what your desired logic was:

df.groupby(['org']).mean().groupby(['cluster']).mean()

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