Python Calculations, using tuples, lists. Python 2.7

Question

Okay so to start off. I have a list of tuples that have a user and then a list of their book ratings as the second item. For example:

[('Ben', [5, 0, 0, 0, 0, 0, 0, 1, 0, 1, -3, 5, 0, 0, 0, 5, 5, 0, 0, 0, 0, 5, 0, 0, 0, 0, 0, 0, 0, 0, 1, 3, 0, 1, 0, -5, 0, 0, 5, 5, 0, 5, 5, 5, 0, 5, 5, 0, 0, 0, 5, 5, 5, 5, -5]),
('Moose', [5, 5, 0, 0, 0, 0, 3, 0, 0, 1, 0, 5, 3, 0, 5, 0, 3, 3, 5, 0, 0, 0, 0, 0, 5, 0, 0, 0, 0, 0, 3, 5, 0, 0, 0, 0, 0, 5, -3, 0, 0, 0, 5, 0, 0, 0, 0, 0, 0, 5, 5, 0, 3, 0, 0])]

That's just for the first two things in the list. Okay so their is a total of 86 users and their ratings in the list. I need to figure out how to be able to multiply all of Ben's ratings times all of Mooses' ratings and then add them all together. For example Ben's first rating is 5 and Moose' first rating is 5 so I do 5x5 and then add that to the list of similarity scores. My problem is that I don't know how to multiply all the elements of the rating list times the rating list of the inputted user. So I need to basically, prompt for a username and then multiply all the other users ratings by the chosen user and output the highest similarity score. Any help at all is appreciated as I am stuck in a rut, thanks in advance.

Sven Marnach · Accepted Answer · 2012-04-12 15:12:39Z

4

You could use NumPy, but a pure-Python solution is also easy:

d = dict(my_list)
sum(map(operator.mul, d["Ben"], d["Moose"]))

The first line is rather unrelated to the problem – it's just to transform your list of tuples to a more appropriate dictionary.

To get the full matrix of similarities, you could use

{name1: {name2: sum(map(operator.mul, d[name1], d[name2])) for name2 in d}
         for name1 in d}

(The latter code snippet only works on Python 2.7 or 3.x.)

edited Apr 12, 2012 at 15:12

answered Apr 12, 2012 at 14:37

Sven Marnach

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9 Comments

Mike Over a year ago

When I try to do either or those two solutions, I get an error: Saying global name 'operator' is not defined.

Sven Marnach Over a year ago

@MichaelLatimer: You have to import operator to use it.

Sven Marnach Over a year ago

@MichaelLatimer: You will need some basic knowledge of Python to take advantage of answers here – consider to work through the Python tutorial.

Mike Over a year ago

Okay I figured that out, guess it should have been obvious, heh.How can I get it to compare Name1(the name input) to the whole list of names?

Sven Marnach Over a year ago

@MichaelLatimer: No idea what it means to compare a name to a list of names.

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