CODEWITHSUNDEEP
pythonpython-3.x
Jared Venson
Jared Venson

Reputation: 57

Error "unsupported operand type(s) for -: 'str' and 'float'?

This code works perfectly to find the average of the numbers in the file it references however I cannot seem to get it to find the standard deviation. The equation for standard deviation is: Square root/(n1-a)^2+(n2-a)^2/m

-everything is under the square root i could not find the character for it

-N1,N2.....Nm=the numbers that are in the list being referenced

-a=average

-m=total number of numbers in the list

here's what I have,

def main():
    numbersFile=open("RandomNumber.txt" , 'r')

    line=numbersFile.readline()
    total=0
    numberoflines=0

    while line != "":
        numberoflines+=1
        total+=int(line)
        line=numbersFile.readline().strip()
    average=total/numberoflines
    std=line-average
    deviation=(std**2)/numberoflines


    print("The average is: " , average)
    print("The standard deviation of the numbers is: " , deviation)


main()

Upvotes: 1

Views: 1602

Answers (3)

Jared Venson
Jared Venson

Reputation: 57

correct source code to calculate:

import math
def main():
numbersFile=open("RandomNumber.txt" , 'r')

line=numbersFile.readline()
total=0
numberoflines=0

while line != "":

    numberoflines+=1
    total+=float(line)


    line=numbersFile.readline().rstrip('\n')
numbersFile.seek(0)
average=total/numberoflines
line=numbersFile.readline()
total=0
while line !="":
    line=float(line)-average
    a=line**2
    total+=a
    line=numbersFile.readline()
std=math.sqrt(total/numberoflines)







print("The average is: " , average)

print("The standard deviation of the numbers is: " , std)


main()

Upvotes: 0

Cezar Cobuz
Cezar Cobuz

Reputation: 1207

Have a look at this question regarding try/except and isdigit(), after that do some casts to float before computing the deviation, something like this:

std=float(line)-float(average)
deviation=float((std**2))/float(numberoflines)

Also keep in mind that your line from line=numbersFile.readline() might contain characters that are not digits, double check your input. Because you use line in std=line-average and you know for sure that average is correct, the problem is with line and std gets the wrong value.

Upvotes: 0

blhsing
blhsing

Reputation: 106435

Your line variable is a string returned by file.readline(). You need to convert it to a float first before you can perform subtraction with another float.

Change:

std=line-average

to:

std=float(line)-average

Upvotes: 2

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