Python如何获取日期令牌的第一个元素

Question

I'm using Python 2.7 and my data looks like this:

import pandas as pd            
df = pd.DataFrame({ 'DateVar' : ['9/1/2013', '10/1/2013', '2/1/2014'],
                'Field' : 'foo' })   

I want to parse DateVar to create 2 new fields: a 'month' field and a 'year' field.

I was able to tokenize 'DateVar' via vectorized string method:

df.DateVar.str.split('/')

This is a little closer to what I want, so then I next tried to slice the months [9, 10, 2] using the following code:

df.DateVar.str.split('/')[0]

But unexpectedly, I'm getting:

['9', '1', '2013']

So how can I get a vector of all the months?

Answer 1

If you only need one column, you can use:

df.DateVar.str.split("/").str[0]

If you need the month and day column, use str.extract :

import pandas as pd            
df = pd.DataFrame({ 'DateVar' : ['9/1/2013', '10/1/2013', '2/1/2014'],
                'Field' : 'foo' })   

print df.DateVar.str.extract(r"(?P<month>\d+)/(?P<day>\d+)/\d+").astype(int)

the output:

  month  day
0      9    1
1     10    1
2      2    1

Answer 2

It is because

>>> df.DateVar.str.split('/')
0     [9, 1, 2013]
1    [10, 1, 2013]
2     [2, 1, 2014]

so

>>> df.DateVar.str.split('/')[0]
['9', '1', '2013']

Answer 3

v = [x[0] for x in df.DateVar.str.split('/')]