宽数据框和长数据框之间的转换

将宽数据框转换为长数据框，可以使用melt函数，示例如下：

import pandas as pd

wide_df = pd.DataFrame(
    {'name': ['Alice', 'Bob', 'Charlie'],
     'math_score': [80, 90, 95],
     'english_score': [85, 87, 92],
     'history_score': [90, 88, 93],
    }
)

long_df = pd.melt(
    wide_df,
    id_vars=["name"],
    value_vars=["math_score", "english_score", "history_score"],
    var_name="subject",
    value_name="score"
)

print(long_df)

输出：

       name        subject  score
0     Alice     math_score     80
1       Bob     math_score     90
2   Charlie     math_score     95
3     Alice  english_score     85
4       Bob  english_score     87
5   Charlie  english_score     92
6     Alice  history_score     90
7       Bob  history_score     88
8   Charlie  history_score     93

将长数据框转换为宽数据框，可以使用pivot函数，示例如下：

import pandas as pd

long_df = pd.DataFrame(
    {'name': ['Alice', 'Alice', 'Bob', 'Bob', 'Charlie', 'Charlie'],
     'subject': ['math_score', 'english_score', 'math_score', 
                 'english_score', 'math_score', 'english_score'],
     'score': [80, 85, 90, 87, 95, 92]
    }
)

wide_df = long_df.pivot(
    index="name",
    columns="subject",
    values="score"
).reset_index()

print(wide_df)

输出：

subject     name  english_score  math_score
0          Alice             85          80
1            Bob             87          90
2        Charlie             92          95