使用新键将数据帧转换为字典

Question

我知道如何将数据帧转换为字典，但我不确定如何创建添加了任意键名的字典

假设我有一个如下所示的数据帧

raw_data = {'regiment': ['Nighthawks', 'Nighthawks', 'Nighthawks', 'Nighthawks', 'Dragoons', 'Dragoons', 'Dragoons', 'Dragoons', 'Scouts', 'Scouts', 'Scouts', 'Scouts'],
'company': ['1st', '1st', '2nd', '2nd', '1st', '1st', '2nd', '2nd','1st', '1st', '2nd', '2nd'],
'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', 'company', 'name', 'preTestScore', 'postTestScore'])

df.head()
Out[96]: 
     regiment company      name  preTestScore  postTestScore
0  Nighthawks     1st    Miller             4             25
1  Nighthawks     1st  Jacobson            24             94
2  Nighthawks     2nd       Ali            31             57
3  Nighthawks     2nd    Milner             2             62
4    Dragoons     1st     Cooze             3             70

我想按'name'分组并计算'preTestScore'中的最大值，最后创建一个字典，如下所示

{'Miller': {'maxTestScore': 4},
 'Jacobson': {'maxTestScore': 24}, ...}

在这里，我添加了一个新的键名“maxTestScore”。我怎样才能用任意的密钥名实现这一点？事先非常感谢

Answer 1

可以将dict comprehension与groupby一起使用：

d = {k:{'maxTestScore':v.max()} for k,v in df.groupby('name')['preTestScore']}
print (d)

{'Piger':   {'maxTestScore': 3}, 
 'Milner':  {'maxTestScore': 2}, 
 'Sone':    {'maxTestScore': 31}, 
 'Jacon':   {'maxTestScore': 4},
 'Cooze':   {'maxTestScore': 3}, 
 'Sloan':   {'maxTestScore': 2},
 'Riani':   {'maxTestScore': 2}, 
 'Miller':  {'maxTestScore': 4}, 
 'Ali':     {'maxTestScore': 31}, 
 'Ryaner':  {'maxTestScore': 24}, 
 'Jacobson':{'maxTestScore': 24}}

另一种解决方案：

d = {k:{'maxTestScore':v} for k,v in df.groupby('name')['preTestScore'].max().iteritems()}
print (d)

{'Piger':   {'maxTestScore': 3}, 
 'Milner':  {'maxTestScore': 2}, 
 'Sone':    {'maxTestScore': 31}, 
 'Jacon':   {'maxTestScore': 4},
 'Cooze':   {'maxTestScore': 3}, 
 'Sloan':   {'maxTestScore': 2},
 'Riani':   {'maxTestScore': 2}, 
 'Miller':  {'maxTestScore': 4}, 
 'Ali':     {'maxTestScore': 31}, 
 'Ryaner':  {'maxTestScore': 24}, 
 'Jacobson':{'maxTestScore': 24}}