如何使用计数将数据帧重新采样到新列中并将列聚合到列表中

Question

I have a DataFrame with measurements of the following form:

                           label
2015-01-17 20:58:00.740000    cc
2015-01-19 04:36:00.740000    xy
2015-01-19 09:48:00.740000    ab
2015-01-19 09:52:00.740000    ab
2015-01-20 11:45:00.740000    ab

And want to resample it by days, create a new column with counts and aggregate the labels into a list. Such that I have the following result:

           counts label
2015-01-17    1   [cc]
2015-01-18    0   []
2015-01-19    3   [ab, xy]
2015-01-20    1   [ab]

I'm new to pandas and don't know how to do it. I have read that DataFrame supports lists as column types. I can count the days by DataFrame.resample() and by sum I can put the labels into one string. But this is not sufficient to produce the results.

I have generated the data with

from datetime import datetime, timedelta

from pandas import DataFrame, TimeGrouper
from random import randint, choice

n = 5
rnd_time = lambda: datetime.now() + timedelta(days=randint(0, 3), hours=randint(0, 24))
rnd_label = lambda: choice(['ab', 'cc', 'xyz'])

gen_times = [rnd_time() for _ in range(n)]
gen_labels = [rnd_label() for _ in range(n)]

df = DataFrame({'label': gen_labels}, index=gen_times)

So how can one produce the desired outcome?

Thank you in advance.

Answer 1

You can do:

>>> df['counts'] = df.groupby(level=0).transform('count')
>>> df.resample('D', how={'counts': lambda x: x[0] if len(x) else 0, 
                          'label' : lambda x: list(set(x))})
            count     label
2015-01-17      1      [cc]
2015-01-18      0        []
2015-01-19      3  [xy, ab]
2015-01-20      1      [ab]

EDIT: If the order of the elements is important then replace list(set(x)) with list(OrderedDict.fromkeys(x)) .