从一年的第一天开始对Pandas Dataframe进行每周重新采样

Question

I have a dataframe containing hourly data, i want to get the max for each week of the year, so i used resample to group data by week

weeks = data.resample("W").max()

the problem is that week max is calculated starting the first monday of the year, while i want it to be calculated starting the first day of the year.

I obtain the following result, where you can notice that there is 53 weeks, and the last week is calculated on the next year while 2017 doesn't exist in the data

Date        dots       
2016-01-03  0.647786
2016-01-10  0.917071
2016-01-17  0.667857
2016-01-24  0.669286
2016-01-31  0.645357


Date        dots                
2016-12-04  0.646786
2016-12-11  0.857714
2016-12-18  0.670000
2016-12-25  0.674571
2017-01-01  0.654571

is there a way to calculate week for pandas dataframe starting first day of the year?

Answer 1

One quick remedy is, given you data in one year, you can group it by day first, then take group of 7 days:

new_df = (df.resample("D", on='Date').dots
            .max().reset_index()
         )

new_df.groupby(new_df.index//7).agg({'Date': 'min', 'dots': 'max'})

new_df.head()

Output:

    Date        dots
0   2016-01-01  0.996387
1   2016-01-08  0.999775
2   2016-01-15  0.997612
3   2016-01-22  0.979376
4   2016-01-29  0.998240
5   2016-02-05  0.995030
6   2016-02-12  0.987500

and tail:

    Date        dots
48  2016-12-02  0.999910
49  2016-12-09  0.992910
50  2016-12-16  0.996877
51  2016-12-23  0.992986
52  2016-12-30  0.960348

Answer 2

找到一年的开始日期，例如，假设是星期五，然后您可以指定要重新采样的锚定后缀 ，以便计算从一年的第一天开始的weeks = data.resample("W-FRI").max() ： weeks = data.resample("W-FRI").max()