Download the PDF for Hands On Machine Learning With Scikit-Learn by Aurelien Geron. This book is a great guide for anyone wanting to learn more about machine learning and how to implement it using the Scikit-Learn library.
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In this guide, you will learn about the basic concepts of machine learning as well as how to implement machine learning algorithms using the popular Python library Scikit-Learn. This guide is intended for beginners who are interested in getting started with machine learning. However, some prior knowledge of Python and basic statistical concepts is recommended.
What is Scikit-Learn?
Scikit-learn is a free machine learning library for Python. It features various classification, regression and clustering algorithms, including support vector machines, random forests, gradient boosting, k-means and DBSCAN, and is designed to interoperate with the Python numerical and scientific libraries NumPy and SciPy.
The easiest way to install scikit-learn is using pip
pip install -U scikit-learn
* NumPy >= 1.8.2
* SciPy >= 0.13.3
* joblib >= 0.8 (optional)
If you installed Python from source, with an installer from python.org, you will already have pip and setuptools, but will need to upgrade to the latest version:
On Linux or OS X: pip install -U pip setuptools
On Windows: python -m pip install -U pip setuptools
In this section, we will take a look at how to load some of the most commonly used datasets in both regression and classification from the scikit-learn library. We will also briefly cover how to generate your own synthetic dataset using the make_regression and make_classification functions.
As with most things in Python, loading datasets into scikit-learn is extremely simple. The first step is to import the load_* function that corresponds to the type of dataset you want to load. For example, if we wanted to load the iris dataset, we would use the following code:
from sklearn.datasets import load_iris
iris = load_irirs()
The iris dataset is a classic dataset that is often used for benchmarking machine learning algorithms. It consists of 150 samples of iris flowers from three different species: Iris setosa, Iris virginica, and Iris versicolor. Each sample has four features: sepal length, sepal width, petal length, and petal width. The target variable is the species of the flower, which has been coded as 0 (Iris setosa), 1 (Iris virginica), or 2 (Iris versicolor).
The second step is to call the .data and .target attributes of the loaded dataset object to get the input features and target variable, respectively. For example:
X = iris.data
y = iris setosa) y = 1 (Iris virginica) y = 2 (Iris versicolor) As you can see, our data matrix X has 150 rows (samples) and 4 columns (features), while our target vector y has 150 elements (samples), each of which corresponds to a class label.
Preprocessing data is an important step in any machine learning project. The goal of this step is to prepare the data for modeling, which includes making sure that the data is clean (i.e. no missing values or outliers) and standardized (i.e. all features are on the same scale).
In this chapter, we will go over some common preprocessing techniques, such as imputation ( filling in missing values), scaling ( putting all features on the same scale), and one-hot encoding (converting categorical variables into dummy variables). We will also learn about the Pipeline class in scikit-learn, which can be used to chain together multiple preprocessing steps (and even models!) into one object.
After reading this chapter, you should be able to:
– Understand why preprocessing is important
– Impute missing values using different strategies
– Scale data using different methods
– Perform one-hot encoding on categorical variables
Classification is a supervised task in machine learning where we aim to predict, from a given set of features, what class a new data point should be. In this chapter, we explore various popular classification algorithms andtrain and evaluate them on publicly available datasets. Via these examples, we will understand the major concepts behind different classification approaches and their relative strengths and weaknesses.
We will cover the following topics in this chapter:
– Loading an example dataset
– Understanding the data
– Training a classifier
– Evaluating a classifier
– Visualizing the decision boundary
After training a model, the next step is to evaluate it to see how well it performs on new data. This chapter will show you how to use three different evaluation metrics, and how to select the appropriate metric for a given task.
The first metric we will look at is accuracy. Accuracy is the number of correct predictions divided by the total number of predictions. For classification tasks, this is simply the number of correctly classified examples divided by the total number of examples.
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In machine learning, hyperparameter tuning is the process of selecting the optimal values for a model’s hyperparameters. A model’s hyperparameters determine its structure and capacity and therefore have a significant impact on its performance. Hyperparameter tuning is a critical step in the machine learning process, and can often lead to substantial improvements in model performance.
There are a few different methods for hyperparameter tuning, but the most common is grid search. Grid search involves specifying a list of values for each hyperparameter and then training and evaluating a model for each combination of values. The best combination of values is then selected as the optimal set of hyperparameters for the model.
Grid search can be time-consuming, so it is often helpful to use a randomized search instead. Randomized search randomly sampling from the space of possible values for each hyperparameter, rather than exhaustively searching through all possible combinations. This can be much faster than grid search while still yielding good results.
Another method for hyperparameter tuning is Bayesian optimization. Bayesian optimization uses Bayesian inference to find the optimal set of hyperparameters for a model. This method can be more efficient than grid search or randomized search, but it can also be more difficult to implement.
No matter which method you use,hyperparameter tuning is an essential part of building machine learning models. By taking the time to tune your models’ hyperparameters, you can ensuring that they are performing at their best.
Saving and Loading Models
After training a model, you will want to save it to use later. To do this, you can use the `joblib` library:
from joblib import dump, load
To load the model back:
model = load(‘filename.joblib’)
Congratulations on completing this course!
We hope you enjoyed learning about hands-on machine learning with scikit-learn. If you found this course helpful, we encourage you to continue your learning journey by checking out our other courses and resources.
Here are some next steps we recommend:
If you want to dive deeper into machine learning, we recommend our course, Supervised Learning with scikit-learn.
To learn more about working with data in Python, we recommend our course, Python for Data Science: Fundamental Techniques for Analytics.
If you want to learn more about the theoretical underpinnings of machine learning, we recommend our course, Machine Learning: Supervised and Unsupervised Approaches.
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