Question

我有这个DataFrame：

               Pred
Date               
2002-03-01 -0.03729
2002-04-01  0.11047
2002-05-01  0.02842
2002-06-01  0.01005
2002-07-01 -0.03607
2002-08-01  0.07484
...

我使用以下功能：

def lag(df):
    df.columns=['Value']
    df.sort_index(ascending=True)

    df['1lag']=df.Value.shift(1)
    df['2lag']=df.Value.shift(2)
    df['3lag']=df.Value.shift(3)
    df['4lag']=df.Value.shift(4)

它一直给我同样的警告：

See the caveats in the documentation: http://pandas.pydata.org/pandas-docs/stable/indexing.html#indexing-view-versus-copy
df['1lag']=df.Value.shift(1)
/Users/file.py:1020: 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

每个df.Value.shift命令都会发出一个警告。任何想法为什么会发生？

Answer 1

试试这个：

def lag(df):
    df.columns=['Value']
    df.sort_index(ascending=True)

    df = df.assign(lag1=df.Value.shift(1))
    df = df.assign(lag2=df.Value.shift(2))
    df = df.assign(lag3=df.Value.shift(3))
    df = df.assign(lag4=df.Value.shift(4))
    return df

警告：正在尝试在DataFrame的切片副本上设置值

1 个答案: