从 Pandas 的前一行中查找值

Question

I have the following dataframe

Date             UUID         Value         RANK
01/03/2019        A            0              2
28/02/2019        A            1              1
28/02/2019        B            2              2 
26/02/2019        B            3              1
24/02/2019        C            4              2
21/02/2019        C            1              1

And I want to get the following:

Date             UUID         Value         RANK     PreValue
01/03/2019        A            0              2       1
28/02/2019        A            1              1       N/A
28/02/2019        B            2              2       3
26/02/2019        B            3              1       N/A
24/02/2019        C            4              2       1
21/02/2019        C            1              1       N/A

How would I go about getting the previous value?

Any Help would be greatly appreciated.

EDIT: So effectively what I want to do is shift the value based on the rank and uuid

Answer 1

You were almost there, just missing the .groupby :

df['PrevValue'] = df.sort_values(['UUID', 'RANK']).groupby('UUID').Value.shift(1)

print(df)
         Date UUID  Value  RANK  PrevValue
0  01/03/2019    A      0     2        1.0
1  28/02/2019    A      1     1        NaN
2  28/02/2019    B      2     2        3.0
3  26/02/2019    B      3     1        NaN
4  24/02/2019    C      4     2        1.0
5  21/02/2019    C      1     1        NaN

Answer 2

A fun way , using idxmax with drop , the just shift whole Value and condition assign

df.loc[df.index.drop(df.groupby('UUID').RANK.idxmin()),'New']=df.Value.shift(-1)
df
         Date UUID  Value  RANK  New
0  01/03/2019    A      0     2  1.0
1  28/02/2019    A      1     1  NaN
2  28/02/2019    B      2     2  3.0
3  26/02/2019    B      3     1  NaN
4  24/02/2019    C      4     2  1.0
5  21/02/2019    C      1     1  NaN