blog page - 1/1¶
Nogil, numpy, cython¶
I had to implement a custom criterion to optimize a decision tree and I wanted to leverage scikit-learn instead of rewriting my own. Version 0.21 of scikit-learn introduced some changed in the API which make possible to overload an existing criterion and replace some of the logic by another one: _criterion.pyx. The purpose was to show that a fast implementation requires some tricks (see Custom DecisionTreeRegressor adapted to a linear regression) and piecewise_tree_regression_criterion.pyx, piecewise_tree_regression_criterion_fast.pyx for the code. Other than that, every function to overlaod is marked as nogil. Every function or method marked as nogil cannot go through the GIL (see also PEP-0311), which no python object can be created in that method. In fact, no python can be called inside a Cython method protected with nogil. The issue with that is that any numpy method cannot be called.
Faster Polynomial Features¶
The current implementation of
in scikit-learn computes each new feature
independently and that increases the number of
data exchanged between numpy and Python.
The idea of the implementation in
is to reduce this number by brodcast multiplications.
The second optimization occurs by transposing the matrix:
dense matrix are organized by rows in memory so
it is faster to mulitply two rows than two columns.
See Faster Polynomial Features.
Piecewise Linear Regression¶
I decided to turn one of the notebook I wrote about
Piecewise Linear Regression.
I wanted to turn my code into something usable and following
the scikit-learn API:
and another notebook Piecewise linear regression with scikit-learn predictors.
t-SNE is quite an interesting tool to
visualize data on a map but it has one drawback:
results are not reproducible. It is much more powerful
than a PCA but the results is difficult to
interpret. Based on some experiment, if t-SNE
manages to separate classes, there is a good chance that
a classifier can get good performances. Anyhow, I implemented
a regressor which approximates the t-SNE outputs
so that it can be used as features for a further classifier.
I create a notebook Predictable t-SNE and a new tranform
Quantile regression with scikit-learn.¶
scikit-learn does not have any quantile regression.
statsmodels does have one
but I wanted to try something I did for my teachings
based on Iteratively reweighted least squares.
I thought it was a good case study to turn a simple algorithm into
a learner scikit-learn can reused in a pipeline.
The notebook Quantile Regression demonstrates it
and it is implemented in
Function to get insights on machine learned models¶
Machine learned models are black boxes. The module tries to implements some functions to get insights on machine learned models.