计算并返回列表中仅正值的平均值

Question

Ignore all the negative elements, and only use positive elements to calculate average.

ave_pos([3, -3, 4, 0, 2, -1]) = 3

Here is what I have so far and I am completely lost on why it's not working!

def ave_pos(nums):
    avg = 0 
    for x in nums:
       if x > 0:
           avg = avg + x
    return avg

Answer 1

use filter and sum for this:-

a = [3, -3, 4, 0, 2, -1]
apositive = filter(lambda x:x>0, a)
sum(apositive)/len(apositive)

Answer 2

The problem is that you are just adding up all the positive elements, not computing their average. Your variable avg ends up with the sum of all positive elements. To get the average, you need to divide the sum by how many there were. Here's a modification of your code that works:

def ave_pos(nums):
    total = 0
    count = 0
    for x in nums:
       if x > 0:
           total += x
           count += 1
    return float(total) / count

As you can see, it maintains the running total and count separately, and divides them out at the end. If you're using Python 2, then you need the call to float otherwise the division will round down to the next integer. In Python 3 this isn't necessary.

Answer 3

You can use a list comprehension to extract all the positive numbers into another list.

def mean_positive(L):
    # Get all positive numbers into another list
    pos_only = [x for x in L if x > 0]
    if pos_only:
        return sum(pos_only) /  len(pos_only)
    raise ValueError('No postive numbers in input')

Answer 4

A little bit more and your problem can be solved by yourself: you just need to divide the sum by the number of the positive elements:

def ave_pos(nums):
    avg = 0
    pos = 0
    for x in nums:
        if x > 0:
            pos = pos + 1
            avg = avg + x
    avg = avg / pos
    return avg

Answer 5

the formula to calculate average is total_sum / number_of_elements

Use a count variable to count no of positive element and return sum/count

count =0;
sum = 0 
for x in nums:
   if x > 0:
       sum = sum + x
       count = count + 1
return avg/count