Manhattan Distance Recommending system Python

Question

So I've been trying this for a while now but just can't get it work. If you look in the picture you see 2 people in the x and y axes and both are the ratings they gave to movies. And the question is how can I calculate the manhattan distance between these to people.

enter image description here

so this is what I already have... edit i forgot to say that prefs is a dict with personname as key and and a second dict as the value. second dict contains movies as key and rating as value.. and the person1 and 2 are just strings with name which can be found in prefs

def sum_manhattan(prefs,person1,person2):
    """Calculates the Manhattan distance between two critics"""
    total = 0
    ##assume person1 is the x axes and person 2 is the y axes
    x = prefs[person1]
    y = prefs[person2]

    for movie in x:
        if movie in y:
            total = abs(x[movie]-y[movie])
    return total

any help is welcome :)

What exactly is not working? I see that in the loop you do total = abs(...). Is that what you do in your program or is it something you mistyped in the question? — civilu
– civilu, Commented Apr 17, 2013 at 14:36
Are we to assume that prefs, person1, and person2 are structured the same as they are in Programming Collective Intelligence (where the image was lifted from)? answers.oreilly.com/topic/… — Alkini
– Alkini, Commented Apr 17, 2013 at 14:39
i'm sorry.. yes that is exactly what it is but it is what my professor gave me and i forgot to say that prefs is a dict with personname as key and and a second dict as the value. second dict contains movies as key and rating as value.. and the person1 and 2 are just strings with name which can be found in prefs — Musti Hakan
– Musti Hakan, Commented Apr 17, 2013 at 14:52

civilu · Accepted Answer · 2013-04-17 15:07:13Z

1

Based on the link posted by Alkini, I'd say that you should replace

total = abs(x[movie]-y[movie])

with

total += abs(x[movie]-y[movie])

to make things work.

What the code you posted does is return the absolute value of the difference between the ratings of the last movie, while I think you need to add the ratings differences for all movies.

answered Apr 17, 2013 at 15:07

civilu

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1 Comment

Musti Hakan Over a year ago

arg yea that is it! it's very stupid of me not to have seen that :P but anyways thank you!

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