Python pandas convert datetime to timestamp effectively through dt accessor

问题

I have a dataframe with some (hundreds of) million of rows. And I want to convert datetime to timestamp effectively. How can I do it?

My sample df:

df = pd.DataFrame(index=pd.DatetimeIndex(start=dt.datetime(2016,1,1,0,0,1),
    end=dt.datetime(2016,1,2,0,0,1), freq='H'))\
    .reset_index().rename(columns={'index':'datetime'})

df.head()

             datetime
0 2016-01-01 00:00:01
1 2016-01-01 01:00:01
2 2016-01-01 02:00:01
3 2016-01-01 03:00:01
4 2016-01-01 04:00:01

Now I convert datetime to timestamp value-by-value with .apply() but it takes a very long time (some hours) if I have some (hundreds of) million rows:

df['ts'] = df[['datetime']].apply(lambda x: x[0].timestamp(), axis=1).astype(int)

df.head()

             datetime          ts
0 2016-01-01 00:00:01  1451602801
1 2016-01-01 01:00:01  1451606401
2 2016-01-01 02:00:01  1451610001
3 2016-01-01 03:00:01  1451613601
4 2016-01-01 04:00:01  1451617201

The above result is what I want.

If I try to use the .dt accessor of pandas.Series then I get error message:

df['ts'] = df['datetime'].dt.timestamp

AttributeError: 'DatetimeProperties' object has no attribute 'timestamp'

If I try to create eg. the date parts of datetimes with the .dt accessor then it is much more faster then using .apply():

df['date'] = df['datetime'].dt.date

df.head()

             datetime          ts        date
0 2016-01-01 00:00:01  1451602801  2016-01-01
1 2016-01-01 01:00:01  1451606401  2016-01-01
2 2016-01-01 02:00:01  1451610001  2016-01-01
3 2016-01-01 03:00:01  1451613601  2016-01-01
4 2016-01-01 04:00:01  1451617201  2016-01-01

I want something similar with timestamps...

But I don't really understand the official documentation: it talks about "Converting to Timestamps" but I don't see any timestamps there; it just talks about converting to datetime with pd.to_datetime() but not to timestamp...

pandas.Timestamp constructor also doesn't work (returns with the below error):

df['ts2'] = pd.Timestamp(df['datetime'])

TypeError: Cannot convert input to Timestamp

pandas.Series.to_timestamp also makes something totally different that I want:

df['ts3'] = df['datetime'].to_timestamp

df.head()

             datetime          ts                                                ts3
0 2016-01-01 00:00:01  1451602801  <bound method Series.to_timestamp of 0    2016...
1 2016-01-01 01:00:01  1451606401  <bound method Series.to_timestamp of 0    2016...
2 2016-01-01 02:00:01  1451610001  <bound method Series.to_timestamp of 0    2016...
3 2016-01-01 03:00:01  1451613601  <bound method Series.to_timestamp of 0    2016...
4 2016-01-01 04:00:01  1451617201  <bound method Series.to_timestamp of 0    2016...

Thank you!!

回答1:

I think you need convert first to numpy array by values and cast to int64 - output is in ns, so need divide by 10 ** 9:

df['ts'] = df.datetime.values.astype(np.int64) // 10 ** 9
print (df)
              datetime          ts
0  2016-01-01 00:00:01  1451606401
1  2016-01-01 01:00:01  1451610001
2  2016-01-01 02:00:01  1451613601
3  2016-01-01 03:00:01  1451617201
4  2016-01-01 04:00:01  1451620801
5  2016-01-01 05:00:01  1451624401
6  2016-01-01 06:00:01  1451628001
7  2016-01-01 07:00:01  1451631601
8  2016-01-01 08:00:01  1451635201
9  2016-01-01 09:00:01  1451638801
10 2016-01-01 10:00:01  1451642401
11 2016-01-01 11:00:01  1451646001
12 2016-01-01 12:00:01  1451649601
13 2016-01-01 13:00:01  1451653201
14 2016-01-01 14:00:01  1451656801
15 2016-01-01 15:00:01  1451660401
16 2016-01-01 16:00:01  1451664001
17 2016-01-01 17:00:01  1451667601
18 2016-01-01 18:00:01  1451671201
19 2016-01-01 19:00:01  1451674801
20 2016-01-01 20:00:01  1451678401
21 2016-01-01 21:00:01  1451682001
22 2016-01-01 22:00:01  1451685601
23 2016-01-01 23:00:01  1451689201
24 2016-01-02 00:00:01  1451692801

to_timestamp is used for converting from period to datetime index.

回答2:

I think you should not use apply, simply astype would be fine:

df['ts'] = df.datetime.astype('int64') // 10**9

回答3:

There's also another method to do this using the "hidden" attribute of DatetimeIndex called asi8, which creates an integer timestamp.

pd.DatetimeIndex(df.datetime).asi8

Wes McKinney suggested it in this tangentially related stackoverflow question linked here

回答4:

If you don't want to use numpy you can use pure pandas conversions

df['ts'] = pd.to_timedelta(df['datetime'], unit='ns').dt.total_seconds().astype(int)

回答5:

One option would be to use a lambda expressions like such

df['datetime'] = df['datetime'].apply(lambda x: pd.Timestamp(x))

来源：https://stackoverflow.com/questions/40881876/python-pandas-convert-datetime-to-timestamp-effectively-through-dt-accessor

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python

datetime

pandas

timestamp