get the average of some ranges of dates in pandas

Question

I need to group the data by customer_id and get the average of purchase dates intervals. My data looks like this:

date        customer_id
1/1/2020        1
1/2/2020        2
1/3/2020        3
1/4/2020        1
1/5/2020        2
1/1/2021        1
1/2/2021        2
1/3/2021        3

So I need to see what is the average date ranges for each customer. The desired output is:

customer_id        Average_date_ranges(in months)
    1                       7
    2                       5
    3                       12

Answer 1

A simple approximation using groupby_apply could be:

>>> df.groupby('customer_id', as_index=False)['date'] \
      .apply(lambda x: round(x.diff().mean().days / 30, 0))

   customer_id  date
0            1   6.0
1            2   6.0
2            3  12.0