How to calculate cosine similarity between two lists using Pythong?

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I need to calculate the cosine similarity between two lists, let's say for example list 1 which is dataSetI and list 2 which is dataSetII. I cannot use anything such as numpy or a statistics module. I must use common modules (math, etc) (and the least modules as possible, at that, to reduce time spent).

Let's say dataSetI is [3, 45, 7, 2] and dataSetII is [2, 54, 13, 15]. The length of the lists are always equal.

Of course, the cosine similarity is between 0 and 1, and for the sake of it, it will be rounded to the third or fourth decimal with format(round(cosine, 3)).

Thank you very much in advance for helping.

Dec 17, 2018 in Python by aryya
• 7,370 points

1 answer to this question.

0 votes

You should try SciPy. It has a bunch of useful scientific routines for example, "routines for computing integrals numerically, solving differential equations, optimization, and sparse matrices." It uses the superfast optimized NumPy for its number crunching. See here for installing.

Note that spatial.distance.cosine computes the distance, and not the similarity. So, you must subtract the value from 1 to get the similarity.

from scipy import spatial

dataSetI = [3, 45, 7, 2]
dataSetII = [2, 54, 13, 15]
result = 1 - spatial.distance.cosine(dataSetI, dataSetII)
answered Dec 17, 2018 by charlie_brown
• 7,780 points
What if the array size is different like dataSetI is [3, 45, 7, 2,46,22,19,15] and dataSetII is [2, 54, 13, 15]. Can we still do the similarity comparision??
As far as I remember, the array size needs to be the same. That is, datasetI and datasetII has to be of the same size.

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