Applymap界面操作幾個（二）列

Question

假設我有一個數據幀：

df = pd.DataFrame({'DATE_1':['2010-11-06', '2010-10-07', '2010-09-07', '2010-05-07'], 
         'DATE_2':['2010-12-07', '2010-11-06', '2010-10-07', '2010-08-06']}) 
df['DATE_1'] = pd.to_datetime(df['DATE_1']) 
df['DATE_2'] = pd.to_datetime(df['DATE_2']) 

所以它看起來像：

 DATE_1  DATE_2 
0 2010-11-06 2010-12-07 
1 2010-10-07 2010-11-06 
2 2010-09-07 2010-10-07 
3 2010-05-07 2010-08-06 

我想創造另一列DIFF這是DATE_2 diffrence和DATE_1在幾天或幾個月或幾年。
我想有像一個，這是根據這句話，因爲我將不得不從創建很多列，類似於DIFF很多DATE_X列的接口：

def date_diffrence(x, y, parameter): 
    if !np.isnan(x): 
     return (x-y) 
df['DIFF'] = df.apply(date_diffrence(df['DATE_2'], df['DATE_1'])) 

根據這篇文章：Difference between map, applymap and apply methods in Pandas，在我看來，我無法創建這樣一個通用接口。我對嗎？

Answer 1

看來你需要的功能，無需apply與Series（的df列）作爲參數與dt.days：

def date_diffrence_days(x, y): 
    return (x-y).dt.days 

df['DIFF'] = date_diffrence_days(df['DATE_2'], df['DATE_1']) 
print (df) 
     DATE_1  DATE_2 DIFF 
0 2010-11-06 2010-12-07 31 
1 2010-10-07 2010-11-06 30 
2 2010-09-07 2010-10-07 30 
3 2010-05-07 2010-08-06 91 

什麼是一樣的：

df['DIFF'] = (df['DATE_2'] - df['DATE_1']).dt.days 
print (df) 
     DATE_1  DATE_2 DIFF 
0 2010-11-06 2010-12-07 31 
1 2010-10-07 2010-11-06 30 
2 2010-09-07 2010-10-07 30 
3 2010-05-07 2010-08-06 91 

編輯：

def date_diffrence_days(x, y, parameter): 
    if parameter == 'm': 
     return (x-y).dt.days 
    elif parameter == 's': 
     return (x-y).dt.total_seconds() 

df['DIFF'] = date_diffrence_days(df['DATE_2'], df['DATE_1'], 's') 
print (df) 
     DATE_1  DATE_2  DIFF 
0 2010-11-06 2010-12-07 2678400.0 
1 2010-10-07 2010-11-06 2592000.0 
2 2010-09-07 2010-10-07 2592000.0 
3 2010-05-07 2010-08-06 7862400.0