基于1列或更多列在pandas数据帧中添加/插入值

Question

我有2个数据帧

date       sitename  Auto_name                  AutoCount                         
2012-05-01 chess.com Autobiographer               8
2012-05-05 chess.com Autobiographer               1
2012-05-15 chess.com Autobiographer               3

并且

date       sitename  Stu_name      Student count
2012-05-01 chess.com Student        4
2012-05-02 chess.com Student        2

输出应该如何

date       sitename    Autoname                 AutoCount     Stu_name    Stu_count                     
2012-05-01 chess.com Autobiographer               8            Student       4
2012-05-02 chess.com Autobiographer               0            Student       2
2012-05-05 chess.com Autobiographer               1            Student       0
2012-05-15 chess.com Autobiographer               3            Student       0

我想从第二个到第一个插入名称和学生计数，但是根据日期列。它看起来并不那么困难，但我无法弄清楚这一点。

Answer 1

您可以使用merge函数（请参阅合并数据框的文档：http://pandas.pydata.org/pandas-docs/stable/merging.html）。假设您的数据框名为df1和df2：

In [13]: df = pd.merge(df1, df2, how='outer')

In [14]: df
Out[14]: 
         date   sitename       Auto_name  AutoCount Stu_name  StudentCount
0  2012-05-01  chess.com  Autobiographer          8  Student             4
1  2012-05-05  chess.com  Autobiographer          1      NaN           NaN
2  2012-05-15  chess.com  Autobiographer          3      NaN           NaN
3  2012-05-02  chess.com             NaN        NaN  Student             2

上面使用公共列进行合并（在本例中为date和sitename），但您也可以使用on关键字指定列（请参阅{{3} }）。

在下一步中，您可以根据需要填充NaN值。按照示例输出，可以是：

In [15]: df.fillna({'Auto_name':'Autobiographer', 'AutoCount':0, 'Stu_name':'Student', 'StudentCount':0})
Out[15]: 
         date   sitename       Auto_name  AutoCount Stu_name  StudentCount
0  2012-05-01  chess.com  Autobiographer          8  Student             4
1  2012-05-05  chess.com  Autobiographer          1  Student             0
2  2012-05-15  chess.com  Autobiographer          3  Student             0
3  2012-05-02  chess.com  Autobiographer          0  Student             2