df['time2'] = pd.to_datetime( df['time'], format = "%H:%M:%S", errors="coerce") #create datetime
df['timestart'] = df.iloc[[0]]['time2'] #create start time
df['timediff'] = ( df['time2'] - df['timestart']) #substract start_time from current time
But all I get is
Name: time2, dtype: datetime64[ns]
| time | time2 | timestart | timediff |
|---|---|---|---|
| 09:00:00 | 1900-01-01 09:00:00 | 1900-01-01 09:00:00 | 0 days |
| 10:10:00 | 1900-01-01 10:10:00 | 1900-01-01 09:00:00 | 0 days |
| 11:08:00 | 1900-01-01 11:08:00 | 1900-01-01 09:00:00 | 0 days |
| 12:12:00 | 1900-01-01 12:12:00 | 1900-01-01 09:00:00 | 0 days |
"0 days" isn't what I expect. I need
00:00:00
01:10:00
02:08:00
etc.
df = pd.DataFrame(np.array(["09:00:00","10:10:00","11:08:00","12:12:00","13:09:00","14:09:00","15:09:00","16:01:00","16:46:00"]),columns=['time'])
df['time2'] = pd.to_datetime( df['time'], format = "%H:%M:%S", errors="coerce")
starttime = df['time2'].iloc[0]
df['timediff'] = (df['time2'] - starttime )
If you want total seconds then you can use:
df['timediff']=df['timediff'].dt.total_seconds()
If you needed only time part then(you don't care about days):
df['timediff']=pd.to_datetime(df['timediff'].dt.total_seconds(),unit='s').dt.time
output of df:
time time2 timestart timediff
0 09:00:00 1900-01-01 09:00:00 1900-01-01 09:00:00 0 days 00:00:00
1 10:10:00 1900-01-01 10:10:00 1900-01-01 09:00:00 0 days 01:10:00
2 11:08:00 1900-01-01 11:08:00 1900-01-01 09:00:00 0 days 02:08:00
3 12:12:00 1900-01-01 12:12:00 1900-01-01 09:00:00 0 days 03:12:00