for 循环 python 中的 enumerate() 问题

Question

I have a list that contains indices and a list that contains values. I want to check, whether the value at the given position of the index is bigger or smaller than the value that is at the index-1 position in the list. I then want my function to return the index of the value that is smaller - so either the input index or the input-index-1. For testing purposes I have created these:

indices = [2,5,8,11] 
values = [3,10,15,4,20,30,24,11,10,2,12,8,7] 
my_list = []

I set up a for-loop that does almost what I want but it appends the value itself, not it's index. It looks like this:

for i in indices:
    if values[i] > values[i-1]:
        my_list.append(values[i-1])
    else: 
        my_list.append(values[i])

Which gives the output

my_list = [10, 20, 10, 8]

I then tried using enumerate for this purpose but it returns an error.

my_list1 = []        


for i,x in enumerate(indices):
    if values[i] > values[i-1]:
        my_list1.append(indices[x-1])
    else: 
        my_list1.append(indices[x])

the wanted output would be:

my_list1 = [1,4,8,11] 

Answer 1

You were close, simply use i instead of values[i] to append the index:

for i in indices:
    if values[i] > values[i-1]:
        my_list.append(i-1)
    else: 
        my_list.append(i)