我正在尝试使用Pandas在几个条件下进行布尔索引。我最初的DataFrame称为df
。如果执行以下操作,将得到预期的结果:
temp = df[df["bin"] == 3]
temp = temp[(~temp["Def"])]
temp = temp[temp["days since"] > 7]
temp.head()
但是,如果我这样做(我认为应该是等效的),则不会返回任何行:
temp2 = df[df["bin"] == 3]
temp2 = temp2[~temp2["Def"] & temp2["days since"] > 7]
temp2.head()
知道差异的原因是什么?
使用()
是因为运算符优先级:
temp2 = df[~df["Def"] & (df["days since"] > 7) & (df["bin"] == 3)]
或者,在单独的行上创建条件:
cond1 = df["bin"] == 3
cond2 = df["days since"] > 7
cond3 = ~df["Def"]
temp2 = df[cond1 & cond2 & cond3]
样品:
df = pd.DataFrame({'Def':[True] *2 + [False]*4,
'days since':[7,8,9,14,2,13],
'bin':[1,3,5,3,3,3]})
print (df)
Def bin days since
0 True 1 7
1 True 3 8
2 False 5 9
3 False 3 14
4 False 3 2
5 False 3 13
temp2 = df[~df["Def"] & (df["days since"] > 7) & (df["bin"] == 3)]
print (temp2)
Def bin days since
3 False 3 14
5 False 3 13
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