[FIXED] Pandas: Efficient ways to calculate occupancy rate between check-in and check-out dates

Issue

I have the following toy data

a = pd.DataFrame({"chkin": ["2022-05-22", "2022-05-22", "2022-05-23", "2022-05-24"],
                  "chkout": ["2022-05-25", "2022-05-23", "2022-05-26", "2022-05-27"],
                  "rtype": ["A", "A", "A", "A"],
                  "nbooked": [1, 2, 3, 1],
                  "nrooms": [10, 10, 10, 10]})

b = pd.DataFrame({"chkin": ["2022-05-22", "2022-05-23", "2022-05-23", "2022-05-24"],
                  "chkout": ["2022-05-24", "2022-05-26", "2022-05-24", "2022-05-25"],
                  "rtype": ["B", "B", "B", "B"],
                  "nbooked": [2, 1, 1, 3],
                  "nrooms": [12, 12, 12, 12]})

booking = pd.concat([a, b], axis=0, ignore_index=True, sort=False)
booking["chkin"] = pd.to_datetime(booking["chkin"])
booking["chkout"] = pd.to_datetime(booking["chkout"])

My problem is explained in the following figure

The nbooked refers to the number of booked rooms. Each color bar on calendar represents each row of input data. I would like to calculate occupancy rate for each day starts from the earliest check-in date to the last check-in date. (Assume that occupancy rate for each room type are zeros).

Since each day is possible to have check-in and check-out as shown in the calendar. Combining nbooked directly should not guarantee to get correct answer. May I have suggestions how to effectively calculate

Solution

You could create a date range and then explode it, allowing you to groupby and sum for each day. The creation of the date range and explode will be a bit slow.

This will also only give you dates in the output for which the occupancy is non-zero. If you also need the zeroes, reindex over the list of dates you care about.

booking['chkout_2'] = booking.chkout - pd.offsets.DateOffset(days=1)
booking['dates'] = booking.apply(lambda r: pd.date_range(r.chkin, r.chkout_2, freq='D'), axis=1)

res = (booking.set_index(['rtype', 'nbooked', 'nrooms'])
          .explode('dates')
          .reset_index()
          .groupby(['rtype', 'dates'])
          .agg({'nbooked': 'sum', 'nrooms': 'max'}))

res['occ'] = res['nbooked']/res['nrooms']

---

print(res)

              nbooked  nrooms       occ
rtype dates                                
A     2022-05-22        3      10  0.300000
      2022-05-23        4      10  0.400000
      2022-05-24        5      10  0.500000
      2022-05-25        4      10  0.400000
      2022-05-26        1      10  0.100000
B     2022-05-22        2      12  0.166667
      2022-05-23        4      12  0.333333
      2022-05-24        4      12  0.333333
      2022-05-25        1      12  0.083333

Answered By - ALollz