从另一个具有循环和条件的2d列表中生成2d列表

Question

你好，我在python中很新，我想像c#一样，我不能做一些事情。我有这份前男友的单子。

    data = [["Bob","Algebra",5],["Bob","History",4],["Bob","Physics",7],["Bob","Astronomy",5],["Allen","Algebra",5],["Allen","History",4],["Allen","Physics",7],["Mary","Algebra",5],["Mary","History",3],["Mary","Physics",7],["Mary","Astronomy",8]
]

我是如何做出这个输出的：

MathsPerStudent = [["Bob","Algebra","History","Physics","Astronomy"]
                   ["Allen","Algebra","History","Physics"]
                   ["Mary","Algebra","History","Physics","Astronomy"]]

据我所见，我不能

MathsPerStudents=[[]]
        for i in data:
           for j in MathsPerStudents:
               if data[i][0] == j[0]
               MathsPerStudents.append(j[0][i])

并以某种方式正确地填充MathPerStudents。正如我所看到的，datai不能与ji相比，因为其中一个是list，另一个是int from element。关键在于for循环，如何将(i)用作像数据列表这样的列表中的索引。

Answer 1

使用setdefault

Ex:

data = [["Bob","Algebra",5],["Bob","History",4],["Bob","Physics",7],["Bob","Astronomy",5],["Allen","Algebra",5],["Allen","History",4],["Allen","Physics",7],["Mary","Algebra",5],["Mary","History",3],["Mary","Physics",7],["Mary","Astronomy",8]]
result = {}
for k, sub, _ in data:
    result.setdefault(k, []).append(sub)    #Set first element as key and append subject as value
print([[k] + v for k, v in result.items()])   #Form required list

输出：

[['Bob', 'Algebra', 'History', 'Physics', 'Astronomy'],
 ['Allen', 'Algebra', 'History', 'Physics'],
 ['Mary', 'Algebra', 'History', 'Physics', 'Astronomy']]

Answer 2

您可以这样做(不是一条直线，但可能更容易理解)：

MathsPerStudent = {}
for name, subject, grade in data:
    if name not in MathsPerStudent:
        MathsPerStudent[name] = []
    MathsPerStudent[name].append(subject)

这给了你一本字典：

>>> from pprint import pprint
>>> pprint(MathsPerStudent)
{'Allen': ['Algebra', 'History', 'Physics'],
 'Bob': ['Algebra', 'History', 'Physics', 'Astronomy'],
 'Mary': ['Algebra', 'History', 'Physics', 'Astronomy']}

如果您想要的话，可以将其转换为列表形式，但对于任何您想要实现的目标，使用字典可能会更容易：

MathsPerStudentList = [[name] + subjects for name, subjects in MathsPerStudent.items()]

以下是最后一份清单：

>>> pprint(MathsPerStudentList)                                                                                                                            
[['Bob', 'Algebra', 'History', 'Physics', 'Astronomy'],                                                                                                    
 ['Allen', 'Algebra', 'History', 'Physics'],                                                                                                               
 ['Mary', 'Algebra', 'History', 'Physics', 'Astronomy']]

Answer 3

如果列表是按名称排序的，则可以使用itertools.groupby：

import itertools

data = [["Bob","Algebra",5],["Bob","History",4],["Bob","Physics",7],["Bob","Astronomy",5],["Allen","Algebra",5],["Allen","History",4],["Allen","Physics",7],["Mary","Algebra",5],["Mary","History",3],["Mary","Physics",7],["Mary","Astronomy",8]]

output = []
for student, classes in itertools.groupby(data, key=lambda x: x[0]):
    output.append([student] + [entry[1] for entry in classes])
print(output)