update join pandas-python

Question

如何实现对熊猫本机语句（.apply（）的更新联接？我想从Dataframe1中的PhySci上的Dataframe2更新PSMark]

Dataframe1（tbl_ex）：

|    | Sname   |   Tamil |   English |   Maths |   Science |   Sscience |   PhySci |
|---:|:--------|--------:|----------:|--------:|----------:|-----------:|---------:|
|  0 | Abu     |      35 |        65 |      64 |        98 |         36 |        0 |
|  1 | Eric    |      70 |        54 |      65 |        32 |         58 |       25 |
|  2 | Mani    |      56 |        25 |      32 |        32 |         78 |       10 |
|  3 | Ram     |      80 |        24 |      68 |        54 |         76 |        0 |
|  4 | Tom     |      40 |        26 |      56 |        69 |         42 |       65 |
|  5 | Eva     |      50 |        18 |      56 |        87 |         56 |        0 |

Dataframe2（tbl_fy）：

|    | Sname   |   PSMark |
|---:|:--------|---------:|
|  0 | Tom     |       69 |
|  1 | Ram     |       54 |
|  2 | Mani    |       32 |
|  3 | Eva     |       87 |
|  4 | Sam     |       89 |

我通过sqldf模块实现了此目的

q="""
    UPDATE tbl_ex
    SET
      PhySci = (SELECT tbl_fy.PSMark
                            FROM tbl_fy
                            WHERE tbl_fy.Sname = tbl_ex.Sname )
    WHERE
    EXISTS (
        SELECT *
        FROM tbl_fy
        WHERE tbl_fy.Sname = tbl_ex.Sname );
    """

sqldf.run(q)
print(tbl_ex.to_markdown())

tbl_ex的最终结果：

|    | Sname   |   Tamil |   English |   Maths |   Science |   Sscience |   PhySci |
|---:|:--------|--------:|----------:|--------:|----------:|-----------:|---------:|
|  0 | Abu     |      35 |        65 |      64 |        98 |         36 |        0 |
|  1 | Eric    |      70 |        54 |      65 |        32 |         58 |       25 |
|  2 | Mani    |      56 |        25 |      32 |        32 |         78 |       32 |
|  3 | Ram     |      80 |        24 |      68 |        54 |         76 |       54 |
|  4 | Tom     |      40 |        26 |      56 |        69 |         42 |       69 |
|  5 | Eva     |      50 |        18 |      56 |        87 |         56 |       87 |

Answer 1

用途：

df  = pd.merge(df1, df2, on='Sname', how='left')
df = df.assign(PhySci=df.pop('PSMark').fillna(df['PhySci']).astype(int))

结果：

# print(df)

  Sname  Tamil  English  Maths  Science  Sscience  PhySci
0   Abu     35       65     64       98        36       0
1  Eric     70       54     65       32        58      25
2  Mani     56       25     32       32        78      32
3   Ram     80       24     68       54        76      54
4   Tom     40       26     56       69        42      69
5   Eva     50       18     56       87        56      87