Python 2.7:按天和列值移动数据框 [英] Python 2.7: shift a dataframe by day and a column value

问题描述

我有一个名为 df1 的数据框，如下所示:

I have a dataframe named df1 as following:

df1:

               a   b    id
2010-01-01     2   3    21
2010-01-01     2   4    22
2010-01-01     3   5    23
2010-01-01     4   6    24
2010-01-02     1   4    21
2010-01-02     2   5    22
2010-01-02     3   6    23
2010-01-02     4   7    24
2010-01-03     1   8    21
2010-01-03     2   9    22
2010-01-03     3   10    23
2010-01-03     4   11   24
...........................

我想移动a、b和id的值，第i行的值变成第i+1行的值.可以看到df1，同一个日期有几行，id不一样.我想移动df1，我的意思是2010-01-02的值是基于id的2010-01-03值(我的意思是id 21的2010-01-02值，是2010-01-03 id 21 的值).谢谢！

I want to shift the value of a, b and id, the i rows value become the i+1 rows value. As you can see the df1, the same date have several rows, and the id is different. I want to shift the df1, I mean the 2010-01-02 value to be the 2010-01-03 value based on the id(I mean that 2010-01-02 value of id 21, to be the 2010-01-03 value of id 21). Thanks!

我想要的答案:

                a   b    id
2010-01-01     Nan   Nan    Nan
2010-01-01     Nan   Nan    Nan
2010-01-01     Nan   Nan    Nan
2010-01-01     Nan   Nan    Nan
2010-01-02     2   3    21
2010-01-02     2   4    22
2010-01-02     3   5    23
2010-01-02     4   6    24
2010-01-03     1   4    21
2010-01-03     2   5    22
2010-01-03     3   6    23
2010-01-03     4   7    24
...........................

推荐答案

如果所有组的长度相同(在示例 4 中)并且 DatetimeIndex 已排序:

If all groups are same length (in sample 4) and DatetimeIndex is sorted:

df2 = df.shift((df.index == df.index[0]).sum())
print (df2)
              a    b    id
2010-01-01  NaN  NaN   NaN
2010-01-01  NaN  NaN   NaN
2010-01-01  NaN  NaN   NaN
2010-01-01  NaN  NaN   NaN
2010-01-02  2.0  3.0  21.0
2010-01-02  2.0  4.0  22.0
2010-01-02  3.0  5.0  23.0
2010-01-02  4.0  6.0  24.0
2010-01-03  1.0  4.0  21.0
2010-01-03  2.0  5.0  22.0
2010-01-03  3.0  6.0  23.0
2010-01-03  4.0  7.0  24.0

但是如果需要将索引值移动一天:

But if need shift values of index by one day:

df3 = df.shift(1, freq='D')
print (df3)
            a   b  id
2010-01-02  2   3  21
2010-01-02  2   4  22
2010-01-02  3   5  23
2010-01-02  4   6  24
2010-01-03  1   4  21
2010-01-03  2   5  22
2010-01-03  3   6  23
2010-01-03  4   7  24
2010-01-04  1   8  21
2010-01-04  2   9  22
2010-01-04  3  10  23
2010-01-04  4  11  24

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