Python–元素索引目录
给定一个元素列表，任务是编写一个 python 程序来计算所有元素的所有索引。
示例:
Input: test_list = [7, 6, 3, 7, 8, 3, 6, 7, 8]
Output: {8: [4, 8], 3: [2, 5], 6: [1, 6], 7: [0, 3, 7]}
Explanation: 8 occurs at 4th and 8th index, 3 occurs at 2nd and 5th index and so on.
Input: test_list = [7, 6, 3, 7, 8, 3, 6]
Output: {8: [4], 3: [2, 5], 6: [1, 6], 7: [0, 3]}
Explanation: 8 occurs at 4th index, 3 occurs at 2nd and 5th index and so on.
在这种情况下，我们使用枚举()来获取所有索引，并将其附加到索引列表中以进行值匹配。字典理解用于列表中所有元素的迭代。集()用于不重复获取所有元素。
Python 3
# Python3 code to demonstrate working of
# Index Directory of Elements
# Using dictionary comprehension + enumerate()
# initializing list
test_list = [7, 6, 3, 7, 8, 3, 6, 7, 8]
# printing original list
print("The original list is : " + str(test_list))
# getting each element index values
res = {key: [idx for idx, val in enumerate(test_list) if val == key]
for key in set(test_list)}
# printing result
print("Index Directory : " + str(res))
输出:
The original list is : [7, 6, 3, 7, 8, 3, 6, 7, 8]
Index Directory : {8: [4, 8], 3: [2, 5], 6: [1, 6], 7: [0, 3, 7]}
方法 2 : 使用字典理解+group by()+enumerate()+sorted()+item getter()
在这里，我们使用 groupby() 和 sorted() 对相似的元素进行排序和分组。 itemgetter() 用于从索引中获取按值排序的值，以及使用 enumerate() 提取的值。字典理解用于获得分组结果的成对索引。
Python 3
# Python3 code to demonstrate working of
# Index Directory of Elements
# Using dictionary comprehension + groupby() +
# enumerate() + sorted() + itemgetter()
from itertools import groupby
from operator import itemgetter
# initializing list
test_list = [7, 6, 3, 7, 8, 3, 6, 7, 8]
# printing original list
print("The original list is : " + str(test_list))
# after grouping after sorting
# and rearranging and assigning values with index
res = {key: [idx for idx, _ in groups] for key, groups in groupby(
sorted(enumerate(test_list), key=itemgetter(1)), key=itemgetter(1))}
# printing result
print("Index Directory : " + str(res))
输出:
The original list is : [7, 6, 3, 7, 8, 3, 6, 7, 8]
Index Directory : {3: [2, 5], 6: [1, 6], 7: [0, 3, 7], 8: [4, 8]}
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