pandas之merge

 分别测试了how为空(默认情况)inner,outer,left,right 5种情况，发现默认参数为inner

import pandas as pd
df1=pd.DataFrame({'key': list('bbacd'),'data1':range(5)})
df2=pd.DataFrame({'key': list('aabce'),'data2':range(5)})
print("df1:",df1,sep="\n")
print("df2",df2,sep="\n")
print("inner",pd.merge(df1,df2),sep="\n")
print("inner",pd.merge(df1,df2,how='inner'),sep="\n")
print("outer",pd.merge(df1,df2,how='outer'),sep="\n")
print("left",pd.merge(df1,df2,how='left'),sep="\n")
print("right",pd.merge(df1,df2,how='right'),sep="\n")

实验结果 

df1:
  key  data1
0   b      0
1   b      1
2   a      2
3   c      3
4   d      4
df2
  key  data2
0   a      0
1   a      1
2   b      2
3   c      3
4   e      4
inner
  key  data1  data2
0   b      0      2
1   b      1      2
2   a      2      0
3   a      2      1
4   c      3      3
inner
  key  data1  data2
0   b      0      2
1   b      1      2
2   a      2      0
3   a      2      1
4   c      3      3
outer
  key  data1  data2
0   b    0.0    2.0
1   b    1.0    2.0
2   a    2.0    0.0
3   a    2.0    1.0
4   c    3.0    3.0
5   d    4.0    NaN
6   e    NaN    4.0
left
  key  data1  data2
0   b      0    2.0
1   b      1    2.0
2   a      2    0.0
3   a      2    1.0
4   c      3    3.0
5   d      4    NaN
right
  key  data1  data2
0   a    2.0      0
1   a    2.0      1
2   b    0.0      2
3   b    1.0      2
4   c    3.0      3
5   e    NaN      4