SettingWithCopyWarning是什么意思？

Question

SettingWithCopyWarning:
A value is trying to be set on a copy of a slice from a DataFrame.
Try using .loc[row_indexer,col_indexer] = value instead

See the caveats in the documentation: http://pandas.pydata.org/pand...
c[c["a"]=="a"]["a"]=100

是我写的不规范么？

import pandas as pd

a=["a","b","a","c"]
b=[1,2,3,4]
a=pd.DataFrame(a)
a.columns=["a"]
b=pd.DataFrame(b)
b.columns=["b"]
c=pd.concat([a,b],axis=1)
print(c)
c[c["a"]=="a"]["a"]=100
print(c)

a b
0 a 1
1 b 2
2 a 3
3 c 4
a b
0 a 1
1 b 2
2 a 3
3 c 4

Answer 1

实际上是Pandas的API改了,在你这行:

c[c["a"]=="a"]["a"]=100

改成下面这种形式:

>>> c.loc[c["a"]=="a","a"] = 100
>>> c
     a  b
0  100  1
1    b  2
2  100  3
3    c  4

就可以了。