Rounding milliseconds in Pandas datettime column

Question

I have a pandas dataframe in which one column has datetime data. The format of the timestamps is like

2020-05-05 12:15:33.500000

I want to format/ round the milliseconds to the first decimal point. I am using the following code to format.

df['timestamp'].dt.strftime('%Y-%m-%d %H:%M:%S:%f')

Is there any modification I can do to round the milliseconds? Thank you in advance.

Asked By: Malintha

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Source

Answer 1

You can’t directly. You can however post process it with slicing:

df['timestamp'].dt.strftime('%Y-%m-%d %H:%M:%S:%f').str[:-5]

Answered By: mozway

Answer 2

Slight modification of @mozway’s answer:

>>> import datetime
>>> dt = datetime.datetime.now()
>>> dt
datetime.datetime(2022, 8, 18, 10, 42, 37, 714473)
>>> dt.strftime('%Y-%m-%d %H:%M:%S:%f')[:-5]
'2022-08-18 10:42:37:7'

Answered By: C. Pappy

Answer 3

If you are specifically interested in rounding (not merely truncating down), your Series to the nearest tenth of a second, then:

to Timestamps:

df['timestamp'].dt.round('100ms')  # still a Series of Timestamps

To get a Series of strings (with controlled format) instead of Timestamps, then apply one of the other answers to the above, e.g.:

df['timestamp'].dt.round('100ms').dt.strftime('%Y-%m-%d %H:%M:%S.%f').str[:-5]

Or, faster (between 5x for short Series and 1.6x for 100K values or more):

df['timestamp'].apply(lambda t: t.round('100ms').strftime(
    '%Y-%m-%d %H:%M:%S.%f')[:-5])

Example

df = pd.DataFrame({
    'timestamp': pd.to_datetime([
        '2022-08-18 15:30:00.440000',
        '2022-08-18 15:30:00.46000',
        '2022-08-18 15:30:00.500000',
    ])
})

>>> df
                timestamp
0 2022-08-18 15:30:00.440
1 2022-08-18 15:30:00.460
2 2022-08-18 15:30:00.500

>>> df['timestamp'].dt.round('100ms')
0   2022-08-18 15:30:00.400
1   2022-08-18 15:30:00.500
2   2022-08-18 15:30:00.500
Name: timestamp, dtype: datetime64[ns]

>>> df['timestamp'].dt.round('100ms').dt.strftime(
    '%Y-%m-%d %H:%M:%S.%f').str[:-5]
0    2022-08-18 15:30:00.4
1    2022-08-18 15:30:00.5
2    2022-08-18 15:30:00.5
Name: timestamp, dtype: object

>>> df['timestamp'].apply(lambda t: t.round('100ms').strftime(
...     '%Y-%m-%d %H:%M:%S.%f')[:-5])
0    2022-08-18 15:30:00.4
1    2022-08-18 15:30:00.5
2    2022-08-18 15:30:00.5
Name: timestamp, dtype: object

Answered By: Pierre D

Rounding milliseconds in Pandas datettime column

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