Keep only date part when using pandas.to_datetime

Solution 1:

Since version 0.15.0 this can now be easily done using .dt to access just the date component:

df['just_date'] = df['dates'].dt.date

The above returns a datetime.date dtype, if you want to have a datetime64 then you can just normalize the time component to midnight so it sets all the values to 00:00:00:

df['normalised_date'] = df['dates'].dt.normalize()

This keeps the dtype as datetime64, but the display shows just the date value.

• pandas: .dt accessor
• pandas.Series.dt

Solution 2:

Simple Solution:

df['date_only'] = df['date_time_column'].dt.date

Solution 3:

While I upvoted EdChum's answer, which is the most direct answer to the question the OP posed, it does not really solve the performance problem (it still relies on python datetime objects, and hence any operation on them will be not vectorized - that is, it will be slow).

A better performing alternative is to use df['dates'].dt.floor('d'). Strictly speaking, it does not "keep only date part", since it just sets the time to 00:00:00. But it does work as desired by the OP when, for instance:

• printing to screen
• saving to csv
• using the column to groupby

... and it is much more efficient, since the operation is vectorized.

EDIT: in fact, the answer the OP's would have preferred is probably "recent versions of pandas do not write the time to csv if it is 00:00:00 for all observations".

Solution 4:

Pandas v0.13+: Use to_csv with date_format parameter

Avoid, where possible, converting your datetime64[ns] series to an object dtype series of datetime.date objects. The latter, often constructed using pd.Series.dt.date, is stored as an array of pointers and is inefficient relative to a pure NumPy-based series.

Since your concern is format when writing to CSV, just use the date_format parameter of to_csv. For example:

df.to_csv(filename, date_format='%Y-%m-%d')

See Python's strftime directives for formatting conventions.

Solution 5:

Pandas DatetimeIndex and Series have a method called normalize that does exactly what you want.

You can read more about it in this answer.

It can be used as ser.dt.normalize()