.. DO NOT EDIT. .. THIS FILE WAS AUTOMATICALLY GENERATED BY SPHINX-GALLERY. .. TO MAKE CHANGES, EDIT THE SOURCE PYTHON FILE: .. "auto_examples/kernel_approximation/plot_scalable_poly_kernels.py" .. LINE NUMBERS ARE GIVEN BELOW. .. only:: html .. note:: :class: sphx-glr-download-link-note :ref:`Go to the end ` to download the full example code. or to run this example in your browser via Binder .. rst-class:: sphx-glr-example-title .. _sphx_glr_auto_examples_kernel_approximation_plot_scalable_poly_kernels.py: ====================================================== Scalable learning with polynomial kernel approximation ====================================================== .. currentmodule:: sklearn.kernel_approximation This example illustrates the use of :class:`PolynomialCountSketch` to efficiently generate polynomial kernel feature-space approximations. This is used to train linear classifiers that approximate the accuracy of kernelized ones. We use the Covtype dataset [2], trying to reproduce the experiments on the original paper of Tensor Sketch [1], i.e. the algorithm implemented by :class:`PolynomialCountSketch`. First, we compute the accuracy of a linear classifier on the original features. Then, we train linear classifiers on different numbers of features (`n_components`) generated by :class:`PolynomialCountSketch`, approximating the accuracy of a kernelized classifier in a scalable manner. .. GENERATED FROM PYTHON SOURCE LINES 23-27 .. code-block:: Python # Authors: The scikit-learn developers # SPDX-License-Identifier: BSD-3-Clause .. GENERATED FROM PYTHON SOURCE LINES 28-37 Preparing the data ------------------ Load the Covtype dataset, which contains 581,012 samples with 54 features each, distributed among 6 classes. The goal of this dataset is to predict forest cover type from cartographic variables only (no remotely sensed data). After loading, we transform it into a binary classification problem to match the version of the dataset in the LIBSVM webpage [2], which was the one used in [1]. .. GENERATED FROM PYTHON SOURCE LINES 37-45 .. code-block:: Python from sklearn.datasets import fetch_covtype X, y = fetch_covtype(return_X_y=True) y[y != 2] = 0 y[y == 2] = 1 # We will try to separate class 2 from the other 6 classes. .. GENERATED FROM PYTHON SOURCE LINES 46-52 Partitioning the data --------------------- Here we select 5,000 samples for training and 10,000 for testing. To actually reproduce the results in the original Tensor Sketch paper, select 100,000 for training. .. GENERATED FROM PYTHON SOURCE LINES 52-59 .. code-block:: Python from sklearn.model_selection import train_test_split X_train, X_test, y_train, y_test = train_test_split( X, y, train_size=5_000, test_size=10_000, random_state=42 ) .. GENERATED FROM PYTHON SOURCE LINES 60-66 Feature normalization --------------------- Now scale features to the range [0, 1] to match the format of the dataset in the LIBSVM webpage, and then normalize to unit length as done in the original Tensor Sketch paper [1]. .. GENERATED FROM PYTHON SOURCE LINES 66-74 .. code-block:: Python from sklearn.pipeline import make_pipeline from sklearn.preprocessing import MinMaxScaler, Normalizer mm = make_pipeline(MinMaxScaler(), Normalizer()) X_train = mm.fit_transform(X_train) X_test = mm.transform(X_test) .. GENERATED FROM PYTHON SOURCE LINES 75-81 Establishing a baseline model ----------------------------- As a baseline, train a linear SVM on the original features and print the accuracy. We also measure and store accuracies and training times to plot them later. .. GENERATED FROM PYTHON SOURCE LINES 81-97 .. code-block:: Python import time from sklearn.svm import LinearSVC results = {} lsvm = LinearSVC() start = time.time() lsvm.fit(X_train, y_train) lsvm_time = time.time() - start lsvm_score = 100 * lsvm.score(X_test, y_test) results["LSVM"] = {"time": lsvm_time, "score": lsvm_score} print(f"Linear SVM score on raw features: {lsvm_score:.2f}%") .. rst-class:: sphx-glr-script-out .. code-block:: none Linear SVM score on raw features: 75.62% .. GENERATED FROM PYTHON SOURCE LINES 98-117 Establishing the kernel approximation model ------------------------------------------- Then we train linear SVMs on the features generated by :class:`PolynomialCountSketch` with different values for `n_components`, showing that these kernel feature approximations improve the accuracy of linear classification. In typical application scenarios, `n_components` should be larger than the number of features in the input representation in order to achieve an improvement with respect to linear classification. As a rule of thumb, the optimum of evaluation score / run time cost is typically achieved at around `n_components` = 10 * `n_features`, though this might depend on the specific dataset being handled. Note that, since the original samples have 54 features, the explicit feature map of the polynomial kernel of degree four would have approximately 8.5 million features (precisely, 54^4). Thanks to :class:`PolynomialCountSketch`, we can condense most of the discriminative information of that feature space into a much more compact representation. While we run the experiment only a single time (`n_runs` = 1) in this example, in practice one should repeat the experiment several times to compensate for the stochastic nature of :class:`PolynomialCountSketch`. .. GENERATED FROM PYTHON SOURCE LINES 117-149 .. code-block:: Python from sklearn.kernel_approximation import PolynomialCountSketch n_runs = 1 N_COMPONENTS = [250, 500, 1000, 2000] for n_components in N_COMPONENTS: ps_lsvm_time = 0 ps_lsvm_score = 0 for _ in range(n_runs): pipeline = make_pipeline( PolynomialCountSketch(n_components=n_components, degree=4), LinearSVC(), ) start = time.time() pipeline.fit(X_train, y_train) ps_lsvm_time += time.time() - start ps_lsvm_score += 100 * pipeline.score(X_test, y_test) ps_lsvm_time /= n_runs ps_lsvm_score /= n_runs results[f"LSVM + PS({n_components})"] = { "time": ps_lsvm_time, "score": ps_lsvm_score, } print( f"Linear SVM score on {n_components} PolynomialCountSketch " + f"features: {ps_lsvm_score:.2f}%" ) .. rst-class:: sphx-glr-script-out .. code-block:: none Linear SVM score on 250 PolynomialCountSketch features: 76.55% Linear SVM score on 500 PolynomialCountSketch features: 76.92% Linear SVM score on 1000 PolynomialCountSketch features: 77.79% Linear SVM score on 2000 PolynomialCountSketch features: 78.59% .. GENERATED FROM PYTHON SOURCE LINES 150-157 Establishing the kernelized SVM model ------------------------------------- Train a kernelized SVM to see how well :class:`PolynomialCountSketch` is approximating the performance of the kernel. This, of course, may take some time, as the SVC class has a relatively poor scalability. This is the reason why kernel approximators are so useful: .. GENERATED FROM PYTHON SOURCE LINES 157-170 .. code-block:: Python from sklearn.svm import SVC ksvm = SVC(C=500.0, kernel="poly", degree=4, coef0=0, gamma=1.0) start = time.time() ksvm.fit(X_train, y_train) ksvm_time = time.time() - start ksvm_score = 100 * ksvm.score(X_test, y_test) results["KSVM"] = {"time": ksvm_time, "score": ksvm_score} print(f"Kernel-SVM score on raw features: {ksvm_score:.2f}%") .. rst-class:: sphx-glr-script-out .. code-block:: none Kernel-SVM score on raw features: 79.78% .. GENERATED FROM PYTHON SOURCE LINES 171-178 Comparing the results --------------------- Finally, plot the results of the different methods against their training times. As we can see, the kernelized SVM achieves a higher accuracy, but its training time is much larger and, most importantly, will grow much faster if the number of training samples increases. .. GENERATED FROM PYTHON SOURCE LINES 178-242 .. code-block:: Python import matplotlib.pyplot as plt fig, ax = plt.subplots(figsize=(7, 7)) ax.scatter( [ results["LSVM"]["time"], ], [ results["LSVM"]["score"], ], label="Linear SVM", c="green", marker="^", ) ax.scatter( [ results["LSVM + PS(250)"]["time"], ], [ results["LSVM + PS(250)"]["score"], ], label="Linear SVM + PolynomialCountSketch", c="blue", ) for n_components in N_COMPONENTS: ax.scatter( [ results[f"LSVM + PS({n_components})"]["time"], ], [ results[f"LSVM + PS({n_components})"]["score"], ], c="blue", ) ax.annotate( f"n_comp.={n_components}", ( results[f"LSVM + PS({n_components})"]["time"], results[f"LSVM + PS({n_components})"]["score"], ), xytext=(-30, 10), textcoords="offset pixels", ) ax.scatter( [ results["KSVM"]["time"], ], [ results["KSVM"]["score"], ], label="Kernel SVM", c="red", marker="x", ) ax.set_xlabel("Training time (s)") ax.set_ylabel("Accuracy (%)") ax.legend() plt.show() .. image-sg:: /auto_examples/kernel_approximation/images/sphx_glr_plot_scalable_poly_kernels_001.png :alt: plot scalable poly kernels :srcset: /auto_examples/kernel_approximation/images/sphx_glr_plot_scalable_poly_kernels_001.png :class: sphx-glr-single-img .. GENERATED FROM PYTHON SOURCE LINES 243-252 References ========== [1] Pham, Ninh and Rasmus Pagh. "Fast and scalable polynomial kernels via explicit feature maps." KDD '13 (2013). https://doi.org/10.1145/2487575.2487591 [2] LIBSVM binary datasets repository https://www.csie.ntu.edu.tw/~cjlin/libsvmtools/datasets/binary.html .. rst-class:: sphx-glr-timing **Total running time of the script:** (0 minutes 11.190 seconds) .. _sphx_glr_download_auto_examples_kernel_approximation_plot_scalable_poly_kernels.py: .. only:: html .. container:: sphx-glr-footer sphx-glr-footer-example .. container:: binder-badge .. image:: images/binder_badge_logo.svg :target: https://mybinder.org/v2/gh/scikit-learn/scikit-learn/main?urlpath=lab/tree/notebooks/auto_examples/kernel_approximation/plot_scalable_poly_kernels.ipynb :alt: Launch binder :width: 150 px .. container:: sphx-glr-download sphx-glr-download-jupyter :download:`Download Jupyter notebook: plot_scalable_poly_kernels.ipynb ` .. container:: sphx-glr-download sphx-glr-download-python :download:`Download Python source code: plot_scalable_poly_kernels.py ` .. container:: sphx-glr-download sphx-glr-download-zip :download:`Download zipped: plot_scalable_poly_kernels.zip ` .. include:: plot_scalable_poly_kernels.recommendations .. only:: html .. rst-class:: sphx-glr-signature `Gallery generated by Sphinx-Gallery `_