gudvinr gudvinr - 1 year ago 114
Python Question

Pandas group by chunks not single values

Now I'm kinda confused about grouping stuff using pandas.

I have set of data (over 60k rows) with 3 columns:

2015/12/18 11:12:49 +0300 d1 b1
2015/12/18 11:12:50 +0300 d2 b2
2015/12/18 11:13:08 +0300 d1 b3
2015/12/18 11:13:36 +0300 d2 b4
2015/12/18 11:13:43 +0300 d2 b5
2015/12/18 11:14:21 +0300 d2 c0
2015/12/18 11:14:42 +0300 d2 c1
2015/12/18 11:15:13 +0300 d1 c2
2015/12/18 11:15:19 +0300 d3 c3

And I need to get count of rows grouped by time periods (let's say 0-4, 4-8, 8-12 etc. by 4 hours) and weekdays and then get a single set for periods within a week.

I can get sum for every hour in a week (time is the name of 1st column):

dind = pd.DatetimeIndex(df.time)
gr = df.groupby([dind.weekday, dind.hour])

But I can't figure out how to group by chunks and then merge resulting
into single index column.

I hope it was clear description of the problem.

Answer Source

The first part of you question, how to group by 4 hour chunks is easy and is addressed in both options below. df.index.hour // 4

The second part was vague as there are several ways to interpret "merge into a single column". I provided you two alternatives.

Option 1

gpd = df.groupby([df.index.weekday, df.index.hour // 4]).size()
gpd.index = gpd.index.to_series()

(4, 2)    9
dtype: int64

Option 2

gpd = df.groupby([df.index.weekday, df.index.hour // 4]).size()
gpd.index = ['{}_{}'.format(*i) for i in gpd.index]

4_2    9
dtype: int64
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