Python Pandas - How to perform ceil operation on the DateTimeIndex with milliseconds frequency

To perform a ceil operation on the DateTimeIndex with milliseconds frequency, use the DateTimeIndex.ceil() method. For milliseconds frequency, use the freq parameter with value 'ms'.

What is the Ceil Operation?

The ceil operation rounds timestamps up to the nearest specified frequency. For milliseconds, it rounds up to the next millisecond boundary, removing microseconds and nanoseconds precision.

Syntax

DateTimeIndex.ceil(freq)

Parameters

• freq ? The frequency to round up to. Use 'ms' for milliseconds

Example

Let's create a DateTimeIndex with microsecond precision and apply the ceil operation ?

import pandas as pd

# Create DatetimeIndex with period 5 and frequency as 40 seconds
# The timezone is Australia/Adelaide
datetimeindex = pd.date_range('2021-10-18 07:20:32.261811624', periods=5,
                              tz='Australia/Adelaide', freq='40S')

# Display DateTimeIndex
print("DateTimeIndex...")
print(datetimeindex)

# Display DateTimeIndex frequency
print("\nDateTimeIndex frequency...")
print(datetimeindex.freq)

# Perform ceil operation with milliseconds frequency
print("\nPerforming ceil operation with milliseconds frequency...")
result = datetimeindex.ceil(freq='ms')
print(result)

DateTimeIndex...
DatetimeIndex(['2021-10-18 07:20:32.261811624+10:30',
               '2021-10-18 07:21:12.261811624+10:30',
               '2021-10-18 07:21:52.261811624+10:30',
               '2021-10-18 07:22:32.261811624+10:30',
               '2021-10-18 07:23:12.261811624+10:30'],
              dtype='datetime64[ns, Australia/Adelaide]', freq='40S')

DateTimeIndex frequency...
<40 * Seconds>

Performing ceil operation with milliseconds frequency...
DatetimeIndex(['2021-10-18 07:20:32.262000+10:30',
               '2021-10-18 07:21:12.262000+10:30',
               '2021-10-18 07:21:52.262000+10:30',
               '2021-10-18 07:22:32.262000+10:30',
               '2021-10-18 07:23:12.262000+10:30'],
              dtype='datetime64[ns, Australia/Adelaide]', freq=None)

How It Works

Notice how the original timestamps had microseconds precision (.261811624), but after the ceil operation with 'ms' frequency, they were rounded up to the next millisecond (.262000). The microseconds and nanoseconds were removed.

Key Points

• The ceil() method always rounds up to the next boundary
• Using freq='ms' rounds to millisecond precision
• The operation preserves timezone information
• The resulting DateTimeIndex loses its original frequency

Conclusion

The DateTimeIndex.ceil() method with freq='ms' efficiently rounds timestamps up to millisecond precision. This is useful for data alignment and reducing timestamp precision in time series analysis.