PandasMerge():追加合并列中的数据并替换空值

Question

我想合并到表中，同时用另一个表中的非null值替换一个表的null值。

下面的代码是要合并的表的示例：

# Table 1 (has rows with missing values)
a=['x','x','x','y','y','y']
b=['z', 'z', 'z' ,'w', 'w' ,'w' ]
c=[1,1,1,np.nan, np.nan, np.nan]
table_1=pd.DataFrame({'a':a, 'b':b, 'c':c})
table_1
a   b   c
0   x   z   1.0
1   x   z   1.0
2   x   z   1.0
3   y   w   NaN
4   y   w   NaN
5   y   w   NaN
# Table 2 (new table to be appended to table_1, and would need to use values in column 'c' to replace values in the same column in table_1)
a=['y', 'y', 'y']
b=['w', 'w', 'w']
c=[2,2,2]
table_2=pd.DataFrame({'a':a, 'b':b, 'c':c})
table_2
a   b   c
0   y   w   2
1   y   w   2
2   y   w   2

这是我用来合并这两个表的代码，我得到的输出是

# Merging the two tables
merged_table=pd.merge(table_1, table_2, on=['a', 'b'], how='left')
merged_table

当前输出(我不明白为什么行数增加(：

a   b   c_x c_y
0   x   z   1.0 NaN
1   x   z   1.0 NaN
2   x   z   1.0 NaN
3   y   w   NaN 2.0
4   y   w   NaN 2.0
5   y   w   NaN 2.0
6   y   w   NaN 2.0
7   y   w   NaN 2.0
8   y   w   NaN 2.0
9   y   w   NaN 2.0
10  y   w   NaN 2.0
11  y   w   NaN 2.0

所需输出(用表2中的数值替换表_1中"c"列中的空值(：

a   b   c
0   x   z   1.0
1   x   z   1.0
2   x   z   1.0
3   y   w   2.0
4   y   w   2.0
5   y   w   2.0

Answer 1

try:

out=table_1.append(table_2).dropna(subset=['c']).reset_index(drop=True)
#OR
out=pd.concat([table_1,table_2]).dropna(subset=['c']).reset_index(drop=True)

out:的输出

a   b   c
0   x   z   1.0
1   x   z   1.0
2   x   z   1.0
3   y   w   2.0
4   y   w   2.0
5   y   w   2.0