python - Finding Date difference in list of dates [Pandas] -

assuming following dataset has sorted list of dates:

dates=pd.dataframe(data={'client':['1','2'],                          'date':[['2012-3-10','2012-3-11','2012-3-12','2012-3-13','2012-3-14'],                                  ['2012-3-12','2012-3-13','2012-3-16','2012-3-23']]}) 

i want find average date difference in terms of days so, eg, client '2', average timelag 2.75

starting with:

  client                                               date 0      1  [2012-3-10, 2012-3-11, 2012-3-12, 2012-3-13, 2... 1      2       [2012-3-12, 2012-3-13, 2012-3-16, 2012-3-23] 

you could

dates.groupby('client')['date'].apply(lambda x: [i / np.timedelta64(1, 'd') in np.diff([pd.to_datetime(c) c in x])[0]]) 

to timedelta in days:

client 1    [1.0, 1.0, 1.0, 1.0] 2         [1.0, 3.0, 7.0] 

or

dates.groupby('client')['date'].apply(lambda x: np.mean([i / np.timedelta64(1, 'd') in np.diff([pd.to_datetime(c) c in x])[0]])) 

for mean:

client 1    1.000000 2    3.666667