python - 使用组行创建新的数据框

Question

我想提取组中每个数据帧的行，并从中创建新的数据帧，这样一个新的数据帧仅包含该组的第一行，另一个新的数据帧包含第二行，另一个包含第三行，等等..例如，我的数据框是:

raw_data = {'regiment': ['Nighthawks', 'Nighthawks', 'Nighthawks', 'Nighthawks', 'Dragoons', 'Dragoons', 'Dragoons', 'Dragoons', 'Scouts', 'Scouts', 'Scouts', 'Scouts'],
    'name': ['Miller', 'Jacobson', 'Ali', 'Milner', 'Cooze', 'Jacon', 'Ryaner', 'Sone', 'Sloan', 'Piger', 'Riani', 'Ali'],
    'preTestScore': [4, 24, 31, 2, 3, 4, 24, 31, 2, 3, 2, 3],
    'postTestScore': [25, 94, 57, 62, 70, 25, 94, 57, 62, 70, 62, 70]}
df = pd.DataFrame(raw_data, columns = ['regiment', 'name', 'preTestScore', 'postTestScore'])
df

      regiment      name  preTestScore  postTestScore
0   Nighthawks    Miller             4             25
1   Nighthawks  Jacobson            24             94
2   Nighthawks       Ali            31             57
3   Nighthawks    Milner             2             62
4     Dragoons     Cooze             3             70
5     Dragoons     Jacon             4             25
6     Dragoons    Ryaner            24             94
7     Dragoons      Sone            31             57
8       Scouts     Sloan             2             62
9       Scouts     Piger             3             70
10      Scouts     Riani             2             62
11      Scouts       Ali             3             70

我将其分组为:

gb = df.groupby("regiment")

   regiment   name  preTestScore  postTestScore
8    Scouts  Sloan             2             62
9    Scouts  Piger             3             70
10   Scouts  Riani             2             62
11   Scouts    Ali             3             70
------------------
     regiment      name  preTestScore  postTestScore
0  Nighthawks    Miller             4             25
1  Nighthawks  Jacobson            24             94
2  Nighthawks       Ali            31             57
3  Nighthawks    Milner             2             62
------------------
   regiment    name  preTestScore  postTestScore
4  Dragoons   Cooze             3             70
5  Dragoons   Jacon             4             25
6  Dragoons  Ryaner            24             94
7  Dragoons    Sone            31             57
------------------

我想创建数据框，例如:

第一行的数据框:

    regiment        name         preTestScore  postTestScore
8    Scouts        Sloan              2             62
0    Nighthawks    Miller             4             25
4    Dragoons      Cooze              3             70

第二行的数据框:

   regiment          name        preTestScore  postTestScore
9    Scouts         Piger             3             70
1    Nighthawks    Jacobson           24            94
5    Dragoons       Jacon             4             25

等等。

我正在考虑使用 Group.apply() 但我不太确定。

非常感谢!

Answer 1

您可能可以使用带有 cumcount 的嵌套 groupby 来完成此操作，例如这将对所有第一次出现的团、所有第二次出现的团进行分组，等等:

In []:
[g for _, g in df.groupby(df.groupby('regiment').cumcount())]

Out[]:
[     regiment    name  preTestScore  postTestScore
 0  Nighthawks  Miller             4             25
 4    Dragoons   Cooze             3             70
 8      Scouts   Sloan             2             62,
      regiment      name  preTestScore  postTestScore
 1  Nighthawks  Jacobson            24             94
 5    Dragoons     Jacon             4             25
 9      Scouts     Piger             3             70,
       regiment    name  preTestScore  postTestScore
 2   Nighthawks     Ali            31             57
 6     Dragoons  Ryaner            24             94
 10      Scouts   Riani             2             62,
       regiment    name  preTestScore  postTestScore
 3   Nighthawks  Milner             2             62
 7     Dragoons    Sone            31             57
 11      Scouts     Ali             3             70]