我正在尝试合并两个在键列中都具有NaN的数据框. NaN不等于NaN,但是“键”列中的两个NaN是匹配的.为什么会这样,我如何才能使它们不匹配？我正在使用python 3.6.
df1 = pd.DataFrame({'key': [3,2,1,np.nan,5],'value': np.random.randn(6)})
df2 = pd.DataFrame({'key': [1,3,np.nan],'value': np.random.randn(3)})
df = pd.merge(df1,df2,on='key',how='left')
print(df1)
print(df2)
print(df)
key value
0 3.0 0.642917
1 2.0 1.347245
2 1.0 -1.381299
3 1.0 1.839940
4 NaN 0.770599
5 5.0 -0.137404
key value
0 1.0 0.580794
1 3.0 0.569973
2 NaN -0.078336
key value_x value_y
0 3.0 0.642917 0.569973
1 2.0 1.347245 NaN
2 1.0 -1.381299 0.580794
3 1.0 1.839940 0.580794
4 NaN 0.770599 -0.078336
5 5.0 -0.137404 NaN
np.nan == np.nan
Out[25]: False
最佳答案
我曾经回答过“为什么”部分的问题,您可以在Why does pandas merge on NaN?上阅读更多内容.
df1.merge(df2.dropna(subset=['key']),how='left')
key value_x value_y
0 3.0 -0.177450 -1.879047
1 2.0 0.179939 NaN
2 1.0 -1.033730 -1.433606
3 1.0 1.426648 -1.433606
4 NaN -0.320173 NaN
5 5.0 -1.824740 NaN