CODEWITHSUNDEEP
pythondatetimepandas
Neal Kruis
Neal Kruis

Reputation: 2287

Time arithmetic on pandas series

I have a pandas DataFrame with a column "StartTime" that could be any datetime value. I would like to create a second column that gives the StartTime relative to the beginning of the week (i.e., 12am on the previous Sunday). For example, this post is 5 days, 14 hours since the beginning of this week.

             StartTime
1  2007-01-19 15:59:24
2  2007-03-01 04:16:08
3  2006-11-08 20:47:14
4  2008-09-06 23:57:35
5  2007-02-17 18:57:32
6  2006-12-09 12:30:49
7  2006-11-11 11:21:34

I can do this, but it's pretty dang slow:

def time_since_week_beg(x):
    y = x.to_datetime()
    return pd.Timedelta(days=y.weekday(),
                        hours=y.hour,
                        minutes=y.minute,
                        seconds=y.second
                       )

df['dt'] = df.StartTime.apply(time_since_week_beg)

What I want is something like this, that doesn't result in an error:

df['dt'] = pd.Timedelta(days=df.StartTime.dt.dayofweek,
                        hours=df.StartTime.dt.hour,
                        minute=df.StartTime.dt.minute,
                        second=df.StartTime.dt.second
            )

TypeError: Invalid type <class 'pandas.core.series.Series'>. Must be int or float.

Any thoughts?

Upvotes: 0

Views: 1668

Answers (1)

Alexander
Alexander

Reputation: 109528

You can use a list comprehension:

df['dt'] = [pd.Timedelta(days=ts.dayofweek, 
                         hours=ts.hour, 
                         minutes=ts.minute, 
                         seconds=ts.second) 
            for ts in df.StartTime]

>>> df
            StartTime              dt
0 2007-01-19 15:59:24 4 days 15:59:24
1 2007-03-01 04:16:08 3 days 04:16:08
2 2006-11-08 20:47:14 2 days 20:47:14
3 2008-09-06 23:57:35 5 days 23:57:35
4 2007-02-17 18:57:32 5 days 18:57:32
5 2006-12-09 12:30:49 5 days 12:30:49
6 2006-11-11 11:21:34 5 days 11:21:34

Depending on the format of StartTime, you may need:

...for ts in pd.to_datetime(df.StartTime)

Upvotes: 2

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