简单的python嵌套循环-索引超出范围

Question

When I run the following code, I get an error:

def genSet(nums):
    for i in range(0, len(nums)-1):
        for x in range(0, len(nums)-1):
            if nums[x] == nums[i]:
                del nums[x] 
    return nums

a = [5, 4, 3, 5, 6, 7, 8, 5, 4, 3]  
print genSet(a)

Output:

Traceback (most recent call last):
  File "49.py", line 9, in <module>
    print genSet(a)
  File "49.py", line 4, in genSet
    if nums[x] == nums[i]:
IndexError: list index out of range

As far as I can tell (I replaced the if statement with "print x, i") the two for loops are fine, so why is the index out of range?

Answer 1

don't do del nums[x] , since this way you make nums shorter and thus get an exception.

you can simply make a set out of the list by set_nums = set(nums)

Answer 2

You are removing elements from nums , therefore it becomes shorter and an IndexError occures.

Anyway, your code would remove everything, because every element has as least one identical element in the list (itself!). If you want to create a "unique" list of elements, create a set:

unique_set = set(nums)

and convert it to list again:

unique_list = list(set(nums))

Answer 3

您可以找到数字相同的索引，将列表创建为numpy数组nums = np.array(nums)并使用np.delete命令。

Answer 4

The example you give can be simply replaced by a one-line code:

print set([5, 4, 3, 5, 6, 7, 8, 5, 4, 3])

If I really want filter out the duplicates in a list myself, I would:

nums = sorted([5, 4, 3, 5, 6, 7, 8, 5, 4, 3])
print reduce(lambda x,y:(y not in x and x+[y]) or x, nums, [])