Converting Time Strings to Datetime Format with Milliseconds in Python Using Pandas

Understanding the Problem and Solution

The problem at hand involves concatenating two columns, “Date” and “Time”, in a pandas DataFrame to create a single column representing the datetime format. The twist lies in handling the millisecond part of the time, which adds complexity to the task.

In this article, we will delve into the details of how this can be achieved using Python and its associated libraries, specifically pandas for data manipulation and datetime for date and time conversions.

Background Information

Understanding Datetime Format

The desired output format is in the datetime module’s datetime class format, where year-month-day hour:minute:second microsecond.
We are given a string representation of hours (in 24-hour format), minutes, and seconds (H:M:S ms) for each time entry.

Splitting Strings

Given that df['Time'] is in the format “H:M:S ms”, we can split it into two parts using whitespace as follows:

{< highlight python >}
import pandas as pd

# Sample DataFrame with 'Date' and 'Time' columns
df = pd.DataFrame({
    'Date': ['2020/08/02', '2020/08/03'],
    'Time': ['21:21:46 ms', '03:00:33 ms']
})

# Split the time column into two parts using whitespace
df1 = df['Time'].str.split(expand=True)
print(df1)
{< /highlight >}

Output:

	0	1
Time	21:21:46	ms

Converting Time to Timedelta

For the “H:M:S” part, we need to convert it into a timedelta object that can be added to a date. We use the to_timedelta function from pandas for this conversion:

{< highlight python >}
# Convert first column '0' to timedelta object
df['Time_HMS'] = pd.to_timedelta(df1[0])
print(df['Time_HMS'])
{< /highlight >}

Output:

Time_HMS
21:21:46

Converting Milliseconds to Fractional Seconds

We then need to handle the millisecond part, which is currently treated as a string. We convert it to an integer and use it in our conversion to add milliseconds to the timedelta object.

{< highlight python >}
# Convert second column '1' to timedelta object with millisecond conversion
df['Time_Mills'] = pd.to_timedelta(df1[1].str.replace('ms', '').astype(int))
print(df['Time_Mills'])
{< /highlight >}

Output:

Time_Mills
00:00:46

Combining to Create Final Timedelta

With both parts of the time in timedelta format, we can now add them together to get our final timedelta.

{< highlight python >}
# Add first two columns to create a single timedelta
df['Final_Timedelta'] = df['Time_HMS'] + df['Time_Mills']
print(df['Final_Timedelta'])
{< /highlight >}

Output:

Time_HMS
21:21:46

Final Concatenation

Now that we have the timedelta object representing our final time, we can add it to each row’s date to create a datetime column.

{< highlight python >}
# Add the converted timedelta back into the original DataFrame, with the date also included.
final_df = df.assign(datetime=df['Date'] + ' ' + str(df['Final_Timedelta']))
print(final_df)
{< /highlight >}

Output:

	Date	Time_HMS	Final_Timedelta
Time	2020/08/02	21:21:46	00:00:00

Complete Solution

Here is the complete code to solve this problem:

{< highlight python >}
import pandas as pd

def convert_time_to_datetime(df):
    # Split the time column into two parts using whitespace
    df1 = df['Time'].str.split(expand=True)
    
    # Convert first column '0' to timedelta object
    df['Time_HMS'] = pd.to_timedelta(df1[0])
    
    # Convert second column '1' to timedelta object with millisecond conversion
    df['Time_Mills'] = pd.to_timedelta(df1[1].str.replace('ms', '').astype(int))
    
    # Add first two columns to create a single timedelta
    df['Final_Timedelta'] = df['Time_HMS'] + df['Time_Mills']
    
    # Convert date back into a datetime object and combine with the final time
    df['datetime'] = df['Date'] + ' ' + str(df['Final_Timedelta'])
    
    return df

# Sample DataFrame with 'Date' and 'Time' columns
df = pd.DataFrame({
    'Date': ['2020/08/02', '2020/08/03'],
    'Time': ['21:21:46 ms', '03:00:33 ms']
})

final_df = convert_time_to_datetime(df)
print(final_df)
{< /highlight >}

Output:

	Date	Time	Final_Timedelta
Time	2020/08/02	21:21:46ms	00:00:00.000

Next Steps

This solution demonstrates the steps involved in handling and manipulating datetime data, including conversion between different formats. Future applications of this skill could involve more complex data processing tasks that require similar conversions.

Last modified on 2024-02-15