pandas dataframe resample per day without date time index

For pandas version 0.19.0 and newer you can use the on keyword:

df.resample('H', on='timestamps').mean()

Result:

                      light
timestamps                 
2004-02-28 00:00:00  147.20
2004-02-28 01:00:00  150.88

Here is an approach to resample.

You can use the following method to sample at T interval.

If original data was in every minute, your new resampled data will be at the 2 min interval. You can use 3T, 4T.... any T value that fits your need.

df_2T = df.resample('2T', on = 'timestamp').mean()

For hourly df_hourly = df.resample('60T', on = 'timestamp').mean()

For daily df_daily = df.resample('1440T', on = 'timestamp').mean()

Note: One day has 60*24 = 1440 min

You are right - need DatetimeIndex, TimedeltaIndex or PeriodIndex else error:

TypeError: Only valid with DatetimeIndex, TimedeltaIndex or PeriodIndex, but got an instance of 'Index'

So you have to first reset_index and set_index if original index is important:

print (df.reset_index().set_index('timestamps'))
                     index   light
timestamps                        
2004-02-28 00:58:45      7  150.88
2004-02-28 00:59:45     26  143.52
2004-02-28 01:00:45     34  150.88
2004-02-28 01:01:15     42  150.88
2004-02-28 01:02:15     59  150.88

if not only set_index:

print (df.set_index('timestamps'))
                      light
timestamps                 
2004-02-28 00:58:45  150.88
2004-02-28 00:59:45  143.52
2004-02-28 01:00:45  150.88
2004-02-28 01:01:15  150.88
2004-02-28 01:02:15  150.88

and then resample:

print (df.reset_index().set_index('timestamps').resample('1D').mean())
            index    light
timestamps                
2004-02-28   33.6  149.408