python-3.x - 如何在列上应用函数

Question

我编写了一个函数来确定工作日。当我尝试将其应用到我的数据框时，遇到以下错误。

data['date'].head() 

0    2016-01-01
1    2016-01-01
2    2016-01-01
3    2016-01-01
4    2016-01-01

def weekday_determination(col):
    year, month, day = (int(x) for x in col.split('-'))
    ans = datetime.date(year, month, day)
    return ans.strftime('%A')

data['week_day'] = data['date'].apply(weekday_determination, axis=1)

我遇到以下错误:

TypeError: weekday_determination() got an unexpected keyword argument 'axis'

Answer 1

这里更好用to_datetime与 Series.dt.day_name :

data['week_day'] = pd.to_datetime(data['date']).dt.day_name()

print (data)
         date week_day
0  2016-01-01   Friday
1  2016-01-01   Friday
2  2016-01-01   Friday
3  2016-01-01   Friday
4  2016-01-01   Friday

在您的解决方案中使用 Series.apply ，所以没有参数axis:

data['date'] = data['date'].apply(weekday_determination)

可能的解决方案为 DataFrame.apply :

data['week_day'] = data.apply(lambda x: weekday_determination(x['date']), axis=1)