在Python字典中交换键和值（包含列表）

Question

我有一本带有主题和页码的参考字典，如下所示：

reference = { 'maths': [3, 24],'physics': [4, 9, 12],'chemistry': [1, 3, 15] }

我需要编写反转引用的函数的帮助。 也就是说，返回一个以页码为键的字典，每个字典都有一个相关的主题列表。 例如，在上面的示例上运行的swap（reference）应该返回

{ 1: ['chemistry'], 3: ['maths', 'chemistry'], 4: ['physics'], 
9: ['physics'], 12: ['physics'], 15: ['chemistry'], 24: ['maths'] }

Answer 1

您可以使用defaultdict ：

from collections import defaultdict

d = defaultdict(list)
reference = { 'maths': [3, 24],'physics': [4, 9, 12],'chemistry': [1, 3, 15] }
for a, b in reference.items():   
    for i in b:    
        d[i].append(a)
print(dict(d))

输出：

{1: ['chemistry'], 3: ['maths', 'chemistry'], 4: ['physics'], 9: ['physics'], 12: ['physics'], 15: ['chemistry'], 24: ['maths']}

不从collections导入：

d = {}
for a, b in reference.items():
    for i in b:
        if i in d:
           d[i].append(a)
        else:
           d[i] = [a]

输出：

{1: ['chemistry'], 3: ['maths', 'chemistry'], 4: ['physics'], 9: ['physics'], 12: ['physics'], 15: ['chemistry'], 24: ['maths']}

Answer 2

reference = {'maths': [3, 24], 'physics': [4, 9, 12], 'chemistry': [1, 3, 15]} table = [] newReference = {} for key in reference: values = reference[key] for value in values: table.append((value, key)) for x in table: if x[0] in newReference.keys(): newReference[x[0]] = newReference[x[0]] + [x[1]] else: newReference[x[0]] = [x[1]] print(newReference)