scikit-prune

Prune your sklearn models.

Deep learning libraries offer pruning techniques to ensure that the models are lightweight when they are stored on disk. It's a technique that makes a lot of sense; you often don't need float64 numbers to represent the weights of a machine learning model.

It got me thinking, would such a technique also work in scikit-learn?

Enter scikit-prune

As a demo, let's say that we're dealing with a text classification use-case.

from sklearn.datasets import fetch_20newsgroups

text = fetch_20newsgroups()['data']

Then we might have a pipeline that fetches the sparse tf/idf features from this text and then turns these into a dense representation via SVD.

from sklearn.pipeline import make_pipeline
from sklearn.decomposition import TruncatedSVD
from sklearn.feature_extraction.text import TfidfVectorizer

pipe = make_pipeline(TfidfVectorizer(), TruncatedSVD(300))
pipe.fit(text)

Then we can choose to save this pipeline on disk, preferably via a system like skops.

from skops.io import dump

dump(pipe, "piper-orig.skops")

This results in a 275Mb file on disk, which is actually kind of big, and the most significant chunk of these megabytes are spent on the float64 numpy arrays that belong to the SVD object.

With this library, you can shrink that down a bit.

from skprune import prune 

dump(prune(pipe), "piper-lite.skops")

Now, the file is fair bit lighter, only 126Mb on disk. Which is a step in the right direction. You can get it down even further by saving it as a ZIP file which moves it closer to 41Mb.

Caveats

This technique can save a bunch of disk space for sure, but at least theoretically, it can also lead to some numerical mishaps when you try to apply the pruned pipeline. Always make sure that you check and evaluate the pruned pipeline before doing anything in production with it!

It's also good to remember that your results may certainly vary. In our example the TruncatedSVD component was the culprit because it was dealing with a very large internal matrix. If your pipeline doesn't have very large matrices, you probably won't get big savings in disk space.