Create datetime index in pandas dataframe

Question

  1988   1   1  7.88 15.57 25.00  0.00  0.81  4.02
  1988   1   2  6.50 10.37 24.87  0.00  0.49  4.30
  1988   1   3  6.48 -8.79 21.28  0.00  0.62  3.91

I read the above file as:

df = pd.read_fwf('27_35.txt', header=None, widths=[6,4,4,6,6,6,6,6,6])

The 1st column is year, 2nd column is month and 3rd column is day. How do I create an index out of these 3 columns ('1988-1-1')?

Answer 1

use parse_dates param and pass a list in a list (so it understands that you want to treat the list of columns as a single entity for parsing):

In [83]:
t="""1988   1   1  7.88 15.57 25.00  0.00  0.81  4.02
  1988   1   2  6.50 10.37 24.87  0.00  0.49  4.30
  1988   1   3  6.48 -8.79 21.28  0.00  0.62  3.91"""
df = pd.read_fwf(io.StringIO(t), header=None, widths=[6,4,4,6,6,6,6,6,6], parse_dates=[[0,1,2]])
df

Out[83]:
       0_1_2       3       4      5  6     7     8
0 1988-01-01  7.88 1  5.57 2   5.00  0  0.81  4.02
1 1988-01-02    6.50   10.37  24.87  0  0.49  4.30
2 1988-01-03    6.48   -8.79  21.28  0  0.62  3.91

In [84]:
df.info()
<class 'pandas.core.frame.DataFrame'>
Int64Index: 3 entries, 0 to 2
Data columns (total 7 columns):
0_1_2    3 non-null datetime64[ns]
3        3 non-null object
4        3 non-null object
5        3 non-null float64
6        3 non-null float64
7        3 non-null float64
8        3 non-null float64
dtypes: datetime64[ns](1), float64(4), object(2)
memory usage: 192.0+ bytes

EDIT

To keep the original date columns add param keep_date_col=True

df = pd.read_fwf('27_35.txt', header=None, widths=[6,4,4,6,6,6,6,6,6], parse_dates=[[0,1,2]], keep_date_col=True)

Answer 2

我总是忘记如何处理熊猫的约会......你可以试试这个：

df.index = df.apply(lambda row: datetime.datetime(int(row[0]), int(row[1]), int(row[2])),1)

Answer 3

I would do this:

import pandas as pd
df = pd.DataFrame(data={'Year':[1988, 1988, 1988], 'Month':[1, 1, 1],
                        'Day': [1, 2, 3]})

date = [str(y)+'-'+str(m)+'-'+str(d) for y, m, d in zip(df.Year, df.Month, df.Day)]
df.index = pd.to_datetime(date)

>>> print df
            Day  Month  Year
1988-01-01    1      1  1988
1988-01-02    2      1  1988
1988-01-03    3      1  1988

After that you can drop Day, Month, and Year from your dataframe.