python - 如何在 Python 熊猫中使用 pd.melt

Question

来自 csv 的这个数据框：

id  name    A   B   C   gpa
0   1111    Phineas NaN B   NaN 3.0
1   1113    Tilly   NaN NaN C   2.5
2   1110    Andres  A   NaN NaN 3.8
3   1112    Jax NaN B   NaN 3.2
4   1114    Ray NaN B   NaN 3.1
5   1115    Koda    NaN NaN C   2.4
6   1120    Bruno   A   NaN NaN 3.7
7   1134    Davis   NaN NaN C   2.6
8   1102    Cassie  A   NaN NaN 4.0

我想要输出：

id  name    grade   gpa
0   1111    Phineas B   3.0
1   1113    Tilly   C   2.5
2   1110    Andres  A   3.8
3   1112    Jax     C   3.2
4   1114    Ray     B   3.1
5   1115    Koda    C   2.4
6   1120    Bruno   A   3.7
7   1134    Davis   C   2.6
8   1102    Cassie  A   4.0

那是什么代码？

标签： pythonpandasdataframe

Answer 1

使用combine_firstwith ，在这种情况下drop您不需要：melt

df['grade'] = df['A'].combine_first(df['B']).combine_first(df['C'])
df.drop(['A','B','C'], axis=1, inplace=True)

或者：

df['grade'] = df[['A','B','C']].values[df[['A','B','C']].notnull()]
df.drop(['A','B','C'], axis=1, inplace=True)

---

print(df)
     id     name  gpa grade
0  1111  Phineas  3.0     B
1  1113    Tilly  2.5     C
2  1110   Andres  3.8     A
3  1112      Jax  3.2     B
4  1114      Ray  3.1     B
5  1115     Koda  2.4     C
6  1120    Bruno  3.7     A
7  1134    Davis  2.6     C
8  1102   Cassie  4.0     A