Python行与列之间的交互

Question

我有以下程序:

df = pd.DataFrame({
    'student':['a'] * 3 + ['b'] * 3 + ['c'] * 4,
    'semester':[1, 1, 2, 2, 1, 1, 2, 2, 2, 2],
    'passed_exam':[True, False] * 5,
    'exam': [
        'French', 'English', 'Italian', 'Chinese', 'Russian',
        'German', 'Chinese', 'Spanish', 'English', 'French'
    ]
})

print (df)

      passed_exam   exam      semester student
    0        True   French          1       a
    1       False   English         1       a
    2        True   Italian         2       a
    3       False   Chinese         2       b
    4        True   Russian         1       b
    5       False   German          1       b
    6        True   Chinese         2       c
    7       False   Spanish         2       c
    8        True   English         2       c
    9       False   French          2       c

有人知道如何找到每个学生(通过考试)互动的学生数量吗？

类似这样的事情:

      passed_exam   exam      semester student   total_st
    0        True   French          1       a         1
    1       False   English         1       a         1
    2        True   Italian         2       a         1
    3       False   Chinese         2       b         1
    4        True   Russian         1       b         1
    5       False   German          1       b         1
    6        True   German          2       c         2
    7       False   Spanish         2       c         2
    8        True   English         2       c         2 
    9       False   French          2       c         2

提前谢谢您!

Answer 1

我将“每个学生(通过考试)互动的学生数量”解释为参加同一考试的学生数量。

那么，看起来是这样的:

df1 = (df
       .groupby(["exam","semester"], as_index=False)["student"].agg("count")
       .rename(columns={"student":"total_st"}))
df.merge(df1).sort_values(["semester","student"])

    passed_exam exam    semester    student total_st
0   True    French  1   a   1
1   False   English 1   a   1
5   True    Russian 1   b   1
6   False   German  1   b   1
2   True    Italian 2   a   1
3   False   Chinese 2   b   2
4   True    Chinese 2   c   2
7   False   Spanish 2   c   1
8   True    English 2   c   1
9   False   French  2   c   1