renamed hyperparams to gscv
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#!/usr/bin/env python3
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# -*- coding: utf-8 -*-
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"""
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Created on Sun Mar 20 13:02:54 2022
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@author: tanu
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"""
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# https://machinelearningmastery.com/hyperparameters-for-classification-machine-learning-algorithms/
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#%% LogisticRegression
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# example of grid searching key hyperparametres for logistic regression
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from sklearn.datasets import make_blobs
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from sklearn.model_selection import RepeatedStratifiedKFold
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from sklearn.model_selection import GridSearchCV
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from sklearn.linear_model import LogisticRegression
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# define dataset
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X, y = make_blobs(n_samples=1000, centers=2, n_features=100, cluster_std=20)
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# define models and parameters
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model = LogisticRegression()
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solvers = ['newton-cg', 'lbfgs', 'liblinear']
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penalty = ['l2']
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c_values = [100, 10, 1.0, 0.1, 0.01]
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# define grid search
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grid = dict(solver=solvers,penalty=penalty,C=c_values)
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cv = RepeatedStratifiedKFold(n_splits=10, n_repeats=3, random_state=1)
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grid_search = GridSearchCV(estimator=model, param_grid=grid, n_jobs=-1, cv=cv, scoring='accuracy',error_score=0)
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grid_result = grid_search.fit(X, y)
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# summarize results
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print("Best: %f using %s" % (grid_result.best_score_, grid_result.best_params_))
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means = grid_result.cv_results_['mean_test_score']
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stds = grid_result.cv_results_['std_test_score']
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params = grid_result.cv_results_['params']
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for mean, stdev, param in zip(means, stds, params):
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print("%f (%f) with: %r" % (mean, stdev, param))
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#%% RidgeClassifier
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from sklearn.datasets import make_blobs
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from sklearn.model_selection import RepeatedStratifiedKFold
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from sklearn.model_selection import GridSearchCV
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from sklearn.linear_model import RidgeClassifier
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# define dataset
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X, y = make_blobs(n_samples=1000, centers=2, n_features=100, cluster_std=20)
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# define models and parameters
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model = RidgeClassifier()
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alpha = [0.9, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.1, 1.0]
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# define grid search
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grid = dict(alpha=alpha)
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cv = RepeatedStratifiedKFold(n_splits=10, n_repeats=3, random_state=1)
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grid_search = GridSearchCV(estimator=model, param_grid=grid, n_jobs=-1, cv=cv, scoring='accuracy',error_score=0)
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grid_result = grid_search.fit(X, y)
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# summarize results
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print("Best: %f using %s" % (grid_result.best_score_, grid_result.best_params_))
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means = grid_result.cv_results_['mean_test_score']
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stds = grid_result.cv_results_['std_test_score']
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params = grid_result.cv_results_['params']
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for mean, stdev, param in zip(means, stds, params):
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print("%f (%f) with: %r" % (mean, stdev, param))
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# NOTES:
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# alpha: If all alphas return the same mean, which do you chose?
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# Python seems to chose the first one?
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# https://stats.stackexchange.com/questions/166950/alpha-parameter-in-ridge-regression-is-high
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# The L2 norm term in ridge regression is weighted by the regularization parameter
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# alpha. So, the alpha parameter need not be small. But, for a larger alpha, the
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# flexibility of the fit would be very strict.
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# So, if the alpha value is 0, it means that it is just an Ordinary Least Squares
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# Regression model. So, the larger is the alpha, the higher is the smoothness constraint.
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# So, the smaller the value of alpha, the higher would be the magnitude of the coefficients.
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# Could be that the model does not fit very well. With a very large alpha,
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# the algorithm more or else ignores the IV's and fits a mean. – Placidia
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# @Placidia, yes I would completely agree with your comment. I was just trying to
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# explain the significance of alpha as a parameter (as asked in the question) in
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# Ridge Regression, and how it's change would affect the fit and the coefficients.
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# Thank you for including the point in the comment.
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# ** READ: https://machinelearningcompass.com/machine_learning_models/ridge_regression/
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#%% KNeighborsClassifier
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from sklearn.datasets import make_blobs
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from sklearn.model_selection import RepeatedStratifiedKFold
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from sklearn.model_selection import GridSearchCV
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from sklearn.neighbors import KNeighborsClassifier
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# define dataset
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X, y = make_blobs(n_samples=1000, centers=2, n_features=100, cluster_std=20)
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# define models and parameters
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model = KNeighborsClassifier()
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n_neighbors = range(1, 21, 2)
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weights = ['uniform', 'distance']
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metric = ['euclidean', 'manhattan', 'minkowski']
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#p = [1,2]
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# define grid search
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grid = dict(n_neighbors=n_neighbors,weights=weights,metric=metric)
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cv = RepeatedStratifiedKFold(n_splits=10, n_repeats=3, random_state=1)
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grid_search = GridSearchCV(estimator=model, param_grid=grid, n_jobs=-1, cv=cv, scoring='accuracy',error_score=0)
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grid_result = grid_search.fit(X, y)
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# summarize results
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print("Best: %f using %s" % (grid_result.best_score_, grid_result.best_params_))
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means = grid_result.cv_results_['mean_test_score']
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stds = grid_result.cv_results_['std_test_score']
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params = grid_result.cv_results_['params']
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for mean, stdev, param in zip(means, stds, params):
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print("%f (%f) with: %r" % (mean, stdev, param))
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# NOTES:
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# https://vitalflux.com/k-nearest-neighbors-explained-with-python-examples/
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# https://vitalflux.com/overfitting-underfitting-concepts-interview-questions/
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# Larger value of K ==> model may underfit
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# Smaller value of K ==> the model may overfit.
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#%%Support Vector Machine (SVM)
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# example of grid searching key hyperparametres for SVC
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from sklearn.datasets import make_blobs
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from sklearn.model_selection import RepeatedStratifiedKFold
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from sklearn.model_selection import GridSearchCV
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from sklearn.svm import SVC
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# define dataset
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X, y = make_blobs(n_samples=1000, centers=2, n_features=100, cluster_std=20)
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# define model and parameters
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model = SVC()
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kernel = ['poly', 'rbf', 'sigmoid']
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C = [50, 10, 1.0, 0.1, 0.01]
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gamma = ['scale']
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# define grid search
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grid = dict(kernel=kernel,C=C,gamma=gamma)
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cv = RepeatedStratifiedKFold(n_splits=10, n_repeats=3, random_state=1)
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grid_search = GridSearchCV(estimator=model, param_grid=grid, n_jobs=-1, cv=cv, scoring='accuracy',error_score=0)
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grid_result = grid_search.fit(X, y)
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# summarize results
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print("Best: %f using %s" % (grid_result.best_score_, grid_result.best_params_))
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means = grid_result.cv_results_['mean_test_score']
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stds = grid_result.cv_results_['std_test_score']
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params = grid_result.cv_results_['params']
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for mean, stdev, param in zip(means, stds, params):
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print("%f (%f) with: %r" % (mean, stdev, param))
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# NOTES:
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# https://stats.stackexchange.com/questions/31066/what-is-the-influence-of-c-in-svms-with-linear-kernel
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# SVM terms: hyperplane, C and soft margins
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# hyperplane that can min(max(dist)) of the suppor vectors from tne hyperplane
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# High C ==> increase overfitting
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# Low C ==> increase underfitting
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# But if C is a regularization parameter, why does a high C increase
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# overfitting, when generally speaking regularization is done to
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# mitigate overfitting, i.e., by creating a more general model?
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# C is a regularisation parameter, but it is essentially attached to
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# the data misfit term (the sum of the slack variables) rather than
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# the regularisation term (the margin bit), so a larger value of C
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# means less regularisation, rather than more. Alternatively you can
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# view the usual representation of the rgularisation parameter
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# as 1/C.
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#C is a regularization parameter that controls the trade off
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#between the achieving a low training error and a low testing
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# error that is the ability to generalize your classifier to unseen data.
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# C Parameter is used for controlling the outliers:
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# low C implies ==> we are allowing more outliers
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# high C implies we are allowing fewer outliers.
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