Linear Regression in Python

Question

I am a brand new to programming and am taking a course in Python. I was asked to do linear regression on a data set that my professor gave out. Below is the program I have written (it doesn't work).

from math import *

f=open("data_setshort.csv", "r")
data = f.readlines()
f.close()

xvalues=[]; yvalues=[]

    for line in data:
    x,y=line.strip().split(",")
    x=float(x.strip())
    y=float(y.strip())

    xvalues.append(x)
    yvalues.append(y)

def regression(x,y):
    n = len(x)
    X = sum(x)
    Y = sum(y)

    for i in x:
        A = sum(i**2)
        return A
    for i in x:
        for j in y:
            C = sum(x*y)
        return C
    return C

    D = (X**2)-nA
    m = (XY - nC)/D
    b = (CX - AY)/D

    return m,b

print "xvalues:", xvalues
print "yvalues:", yvalues   

regression(xvalues,yvalues)

I am getting an error that says: line 23, in regression, A = sum (I**2). TypeError: 'float' object is not iterable.

I need to eventually create a plot for this data set (which I know how to do) and for the line defined by the regression. But for now I am trying to do linear regression in Python.

Answer 1

You can't sum over a single float, but you can sum over lists. E. g. you probably mean A = sum([xi**2 for xi in x]) to calculate Sum of each element in x to the power of 2 . You also have various return statements in your code that don't really make any sense and can probably be removed completely, eg return C after the loop. Additionally, multiplication of two variables a and b can only be done by using a*b in python. Simply writing ab is not possible and will instead be regarded as a single variable with name "ab".

The corrected code could look like this:

def regression(x,y):
    n = len(x)
    X = sum(x)
    Y = sum(y)

    A = sum([xi**2 for xi in x])
    C = sum([xi*yi for xi, yi in zip(x,y)])

    D = X**2 - n*A
    m = (X*Y - n*C) / float(D)
    b = (C*X - A*Y) / float(D)

    return (m, b)

Answer 2

You should probably put in something like A += i**2 As you must understand from the error message that you cannot iterate over a float, which means if i=2 you can't iterate over it as it is not a list, but if as you need to sum all the squares of x, you are iterating over x in for i in x and then you add the squares of i i**2 to A A+=i**2 adn then you return A.

Hope this helps!