Reset time part of a pandas timestamp

问题:

How can I reset the time part of a pandas timestamp?

I want to reset time part in value of pandas.Timestamp.
I guess I can do it using the following procedure.

• step 1) Timestamp to datetime type
• step 2) datetime to seconds
• step 3) truncate time part in seconds
• step 4) bring back seconds to Timestamp

Even if my guess is correct, it takes too long to do. Is there a straightforward way to achieve this goal?

In [371]: ts = pd.Timestamp('2014/11/12 13:35')

In [372]: ts

Out[372]: Timestamp('2014-11-12 13:35:00')

In [373]: ts.hour = 0 # <-- this is what I am trying to do.

回答1:

I think you are looking for the replace method (see docs):

In [18]: ts
Out[18]: Timestamp('2014-11-12 13:35:00')

In [19]: ts.replace(hour=0)
Out[19]: Timestamp('2014-11-12 00:35:00')

This is a method inherited from datetime.datetime

If you want to reset the full time part, you specify all parts in replace:

In [20]: ts.replace(hour=0, minute=0, second=0)
Out[20]: Timestamp('2014-11-12 00:00:00')

There is also a DatetimeIndex.normalize method, but this isn't available on the individual Timestamps (I opened an issue for that: https://github.com/pydata/pandas/issues/8794):

In [21]: pd.DatetimeIndex([ts]).normalize()[0]
Out[21]: Timestamp('2014-11-12 00:00:00')

回答2:

Note that the replace method does not change the Timestamp, so if you want to keep the modified Timestamp you have to assign:

In [2]: ts = pd.Timestamp('2014/11/12 13:35')
In [3]: ts.replace(hour=0)
Out[3]: Timestamp('2014-11-12 00:35:00')
In [4]: ts
Out[4]: Timestamp('2014-11-12 13:35:00')

Note: ts is not modified in the code above.

In [5]: ts = ts.replace(hour=0)
In [6]: ts
Out[6]: Timestamp('2014-11-12 00:35:00')

回答3:

Instead of using datetime.datetime, use datetime.date and it will automatically truncate the hour/minute/second for you.

See https://docs.python.org/library/datetime.html#date-objects

回答4:

pd.Timestamp('2014-11-12 13:35') - pd.offsets.Micro(0, normalize=True) == Timestamp('2014-11-12 00:00:00')