Calculate time difference in milliseconds using Pandas

Question

I have a dataframe timings as follows:

    start_ms                     end_ms
0   2020-09-01T08:11:19.336Z     2020-09-01T08:11:19.336Z
1   2020-09-01T08:11:20.652Z     2020-09-01T08:11:20.662Z
2   2020-09-01T08:11:20.670Z     2020-09-01T08:11:20.688Z

I'm trying to calculate the time difference between the start_ms and end_ms of each row in milliseconds, i.e. I wish to get the result

    start_ms                     end_ms                       diff
0   2020-09-01T08:11:19.336Z     2020-09-01T08:11:19.336Z     0
1   2020-09-01T08:11:20.652Z     2020-09-01T08:11:20.662Z     10
2   2020-09-01T08:11:20.670Z     2020-09-01T08:11:20.688Z     18

I can convert the timestamp to datetime column by column, but I'm not sure if the order of the values are retained.

start_ms_time = pd.to_datetime(timings['start_ms'])
end_ms_time = pd.to_datetime(timings['end_ms'])

Is it possible to convert the timestamps to datetime inside timings, and add the time difference column? Do I even need to convert to get the difference? How do I calculate the time difference in milliseconds?

Answer 1

Subtract columns by Series.sub and then use Series.dt.components:

start_ms_time = pd.to_datetime(timings['start_ms'])
end_ms_time = pd.to_datetime(timings['end_ms'])

timings['diff'] = end_ms_time.sub(start_ms_time).dt.components.milliseconds
print (timings)
                   start_ms                    end_ms  diff
0  2020-09-01T08:11:19.336Z  2020-09-01T08:11:19.336Z     0
1  2020-09-01T08:11:20.652Z  2020-09-01T08:11:20.662Z    10
2  2020-09-01T08:11:20.670Z  2020-09-01T08:11:20.688Z    18

Or Series.dt.total_seconds with multiple by 1000 and cast to integers:

timings['diff'] = end_ms_time.sub(start_ms_time).dt.total_seconds().mul(1000).astype(int)
print (timings)
                   start_ms                    end_ms  diff
0  2020-09-01T08:11:19.336Z  2020-09-01T08:11:19.336Z     0
1  2020-09-01T08:11:20.652Z  2020-09-01T08:11:20.662Z    10
2  2020-09-01T08:11:20.670Z  2020-09-01T08:11:20.688Z    18