replace string datetime to epoch in pandas dataframe

Question

My Dataframe looks like:

Time,User,value 2018-03-30T14:18:49.600,U101,23 2018-03-30T14:18:49.800,U102,22 2018-03-30T14:18:50.000,U101,24

I would like to change String timestamp to epoch in milliseconds in column Time in DataFrame. I am able to do that by saving values in list of lists and iterate over each row. But I need an efficient way such that, I can replace String time to epoch time in Dataframe itself. Thanks in advance.

Answer 1

df['Time'] = (df['Time'] - pd.Timestamp("1970-01-01")) // pd.Timedelta('1s')

is the recommended solution from pandas, reference.

example:

import pandas as pd
df = pd.DataFrame()
df['Time'] = pd.date_range('2012-10-08 18:15:05', periods=4, freq='D')
df['Epoch'] = (df['Time'] - pd.Timestamp("1970-01-01")) // pd.Timedelta('1s')
print(df)

output:

                 Time       Epoch
0 2012-10-08 18:15:05  1349720105
1 2012-10-09 18:15:05  1349806505
2 2012-10-10 18:15:05  1349892905
3 2012-10-11 18:15:05  1349979305

Answer 2

I think need convert to_datetime, then to numpy array with cast to int64 and last divide by 10**6 because native format is in nanoseconds:

df['Time'] = pd.to_datetime(df['Time']).values.astype(np.int64) // 10**6
print (df)
            Time  User  value
0  1522419529600  U101     23
1  1522419529800  U102     22
2  1522419530000  U101     24