如何获取列表中从最大到最小的索引？

Question

I am coding a little project in Python:

I want to get the indexes (in a list) from the highest to smallest number in the following list:

list = [20, 30, 24, 26, 22, 10]

The outcome should be:

index_list = [1, 3, 2, 4, 0, 5]

Anyone has an idea of how I could do that? Thanks in advance.

Answer 1

Build the index_list in ascending index order, then call sort() with a Comparator that sorts descending by the value in the list at the given index.

List<Integer> list = Arrays.asList(20, 30, 24, 26, 22, 10);

List<Integer> index = new ArrayList<>(list.size());
for (int i = 0; i < list.size(); i++)
    index.add(i);
index.sort(Comparator.comparing(list::get).reversed());

System.out.println(index);

Output

[1, 3, 2, 4, 0, 5]

Or you can do it in one statement using streams, same result:

List<Integer> index = IntStream.range(0, list.size()).boxed()
                               .sorted(Comparator.comparing(list::get).reversed())
                               .collect(Collectors.toList());

Answer 2

I am pretty new to programming in python, but this seems to work:

list = [20, 30, 24, 26, 22, 10]
list_sorted = list.copy()
list_sorted.sort()

list_index = []
for x in list_sorted:
    list_index.insert(0,list.index(x))

print(list_index)

output:

[1, 3, 2, 4, 0, 5]

Because above will produce incorrect values it there are duplicates, see next:

list = [20, 10, 24, 26, 22, 10]
list_tmp = list.copy()
list_sorted = list.copy()
list_sorted.sort()

list_index = []
for x in list_sorted:
    list_index.insert(0,list_tmp.index(x))
    list_tmp[list_tmp.index(x)] = -1

print(list)
print(list_index)

output:

[20, 10, 24, 26, 22, 10]
[3, 2, 4, 0, 5, 1]

It should not matter if output is [3, 2, 4, 0, 5, 1] or [3, 2, 4, 0, 1, 5] because those indexes refer to the same values.