python - 如何在列表中查找重复项及其索引？

Question

我有一个 list

l=['a','b','c','c','a','d']

输出应该返回列表中的所有重复元素及其索引

输出:

out = {a:['0','4'],c:['2','3']}

我试过了

def nextDuplicates(c):
    dupl_c = dict()
    sorted_ind_c = sorted(range(len(c)), key=lambda x: c[x])
    for i in xrange(len(c) - 1):
        if c[sorted_ind_c[i]] == c[sorted_ind_c[i+1]]:
            dupl_c[ sorted_ind_c[i] ] = sorted_ind_c[i+1]
    return dupl_c

Answer 1

使用 collections.defaultdict + set 迭代来更快地查找大于 1 的计数:

from collections import defaultdict

l = ['a','b','c','c','a','d']

result = defaultdict(list)

for x in set(l):
    if l.count(x) > 1:
        result[x].extend([i for i, y in enumerate(l) if y == x])

print(result)
# defaultdict(<class 'list'>, {'a': [0, 4], 'c': [2, 3]})