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Question about my loop

2 points · submitted Nov 2024 by u/Either_Back_1545 

English = [90, 81, 73, 97, 85, 60, 74, 64, 72, 67, 87, 78, 85, 96, 77, 100, 92, 96]
Classical_Japanese = (71, 90, 79, 70, 67, 66, 60, 83, 57, 85, 93, 89, 78, 74, 65, 78, 53, 80)

def st_dev(x,y,z):
    return math.sqrt(sum((xi-y)**2 for xi in x) /(len(z)-1))

def st_dev2(x,y,z):
        sumsquares = 0
        x = 0
        n = len(z) -1 
        if n < 2:
            return "0"
        while x < n:
            sumsquares += (z[x]- y )**2
            x += 1
        
        variance = sumsquares/n
        return math.sqrt(variance)

The for loop vary 11.580917366893848 
meanwhile
the while loop vary 11.499076405082917

there is  big difference between this two what happen but if i remove minus one the results are the same for some reason
11.254628677422755
11.254628677422756

can you help me what happen to this?

2 comments · 75% upvoted · other discussions

comments

Adrewmc 1 points · Nov 2024

For loops are basically just convenient while loops to the complier.

The reason you get different number is you’s obviously calculating different values

In 

  sum(xi-y) **2 for xi in x)/(len(z)-1))

You always get every value in x

And 

  while x < n: 
        print(x, end = “, “) 
        #code

The while statement never adds the last variable. To prove this put this print statement.

Though you are dividing by the same number, you’re not dumping the same numerator.

Either_Back_1545 [OP] 1 points · Nov 2024

Ohhh thats dope! thanks!