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.

i is a single float, there is no point in summing its square (e.g. what is the sum of 4 * 4) Also you might want to restudy what a return statement does. — Antti Haapala
– Antti Haapala, Commented Apr 30, 2015 at 16:59
this question has nothing to do with linear regression . . . i'd suggest you edit the title. — abcd
– abcd, Commented Apr 30, 2015 at 20:52

aleju · Accepted Answer · 2015-04-30 17:17:34Z

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, e. g. 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)

answered Apr 30, 2015 at 17:17

aleju

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3 Comments

Nathan Neven Over a year ago

Okay, I knew about using * to do multiplication. Forgetting to have done that probably shows how new I am to this.

Nathan Neven Over a year ago

I don't understand what you're doing to calculate A and C. It looks like you are doing a for-loop in one line. What is the difference between the two lines you have and a typical for-loop?

aleju Over a year ago

[xi**2 for xi in x] means: Take every element xi from list x, increase it to the power of 2 (by **2) and then add it to a new list. [xi*yi for xi, yi in zip(x,y)] means: First build a new list of pairs of x and y values by merging lists x and y. The result would be something like [(x1,y1), (x2,y2), ...]. Then take each of these pairs xi and yi, multiply them by xi*yi and then add them to a new list. In both cases you use sum() to calculate the sum of these lists/values. Generating lists this way is more concise and thus usually easier to read once you understood it.

amartya18x · Accepted Answer · 2015-12-09 20:44:26Z

0

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!

answered Dec 9, 2015 at 20:44

amartya18x

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