Python Machine Learning (ML) Plot

Modules containing reusable functions for machine learning visualization plotting

Compatibility

• Python 3.13 or later

Setup

Add Dependency

python3 -m pip install opengood.py-ml-plot

Note: See Release version badge above for the latest version.

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Features

Classification Model Plotting

Set Up and Display 2-D Classification Plot

Set up a 2-D classification model plot then display its result visualization.

Notes:

• The example below uses a dataset to train a logistic regression model then display the plot for the training set
• For feature scaling, if required, implement the feature scaling logic in the feature_scaling lambda
• For predictions, implement the prediction logic in the predict lambda

import os

import numpy as np
import pandas as pd
from matplotlib import pyplot as plt
from matplotlib.colors import ListedColormap
from sklearn.linear_model import LogisticRegression
from sklearn.model_selection import train_test_split
from sklearn.preprocessing import StandardScaler

from src.opengood.py_ml_plot import setup_classification_plot

resource_path = os.path.join(os.path.dirname(__file__), "../resources", "data.csv")
dataset = pd.read_csv(resource_path)

x = dataset.iloc[:, :-1].values
y = dataset.iloc[:, -1].values

x_train, _, y_train, _ = train_test_split(x, y, test_size=0.2, random_state=0)

sc = StandardScaler()
x_train = sc.fit_transform(x_train)

classifier = LogisticRegression(random_state=0)
classifier.fit(x_train, y_train)

setup_classification_plot(
    x=x_train,
    y=y_train,
    cmap=ListedColormap(("salmon", "dodgerblue")),
    title="Logistic Regression",
    x_label="Age",
    y_label="Estimated Salary",
    feature_scale=lambda x_set, y_set: (
        sc.inverse_transform(x_set), y_set
    ),
    predict=lambda x1, x2: (
        classifier.predict(
            sc.transform(
                np.array([x1.ravel(), x2.ravel()]).T)
        ).reshape(x1.shape)
    ),
)

plt.show()

Output

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Visualization Logic

Feature Scale Lambda Logic

feature_scale lambda implementation logic for function setup_classification_plot is as follows:

• Inverse feature scaling is invoked via a featuring scaling object, such as the StandardScalar object sc created earlier for feature scaling
• x_set and y_set are assigned non-feature scaled values of the matrix of features and the dependent variable
  • x_set values are inverted from their feature-scaled values in x
  • y_set values are not inverted and taken directly from y

Predict Lambda Logic

predict lambda implementation logic for function setup_classification_plot is as follows:

• Classifier object classifier method predict is invoked
• Since the values of the reshaped 2D array are not feature scaled, the values are feature scaled via the transform method on the sc object
  • This method call is not required for models that do not require feature scaling
• ravel function from the NumPy library is used to flatten a multidimensional array into a one-dimensional array
  • x1 and x2 are flatten into a 1D array via the ravel function
  • They are then combined via the array function from the NumPy library into a 2D array
  • The result is then reshaped via the reshape function to match the shape of x1

Setup Plot Visualization Logic

Visualization implementation logic for function setup_classification_plot is as follows:

• ListedColormap class from the Matplotlib library creates an object that generates a colormap visual from a list of colors
• If the feature_scale lambda is defined, x_set and y_set are assigned non-feature scaled values of the matrix of features and the dependent variable from the sets using a feature scaling object, such as the StandardScalar object created earlier for feature scaling
  • x_set values are inverted from their feature-scaled values in x
  • y_set values are not inverted and taken directly from y
• If the feature_scale lambda is not defined, x_set and y_set are assigned the values of x and y, respectively
• meshgrid function from the NumPy library returns a tuple of coordinate matrices from coordinate vectors
  • Two sets of matrices (x1 and x2) are returned with coordinate vectors
  • x1
    • arange function is called with a defined start and stop interval
      • x_set[:, 0] returns all the rows for feature x1
      • start parameter
        • Start of an interval
        • x_set[:, 0].min() returns the minimum value for feature x1
        • Value of 10 is subtracted for padding
      • stop parameter
        • End of an interval
        • x_set[:, 0].max() returns the maximum value for feature x1
        • Value of 10 is added for padding
      • step parameter
        • Spacing between values
        • Value of 0.25 is added for spacing
  • x2
    • arange function is called with a defined start and stop interval
      • x_set[:, 1] returns all the rows for feature x2
      • start parameter
        • Start of an interval
        • x_set[:, 1].min() returns the minimum value for feature x2
        • Value of 1000 is subtracted for padding
        • Value of 1000 is used instead of 10 due to the difference in scaling for feature x2 vs. feature x1
      • stop parameter
        • End of interval
        • x_set[:, 1].max() returns the maximum value for feature x2
        • Value of 1000 is added for padding
      • step parameter
        • Spacing between values
        • Value of 0.25 is added for spacing
• The prediction logic implemented in the preodict lambda is executed, and the result is assigned to y_pred, containing the predictions
• contourf function from the Matplotlib library is used for creating filled contour plots
  • It visualizes 3D data in 2D by drawing filled contours representing constant z-values (heights) on an x-y plane
  • These plots are useful for displaying data like temperature distributions, terrain elevations, or any scalar field where the magnitude varies over 2 dimensions
  • The most basic use case of contourf involves providing a 2D array representing the z-values
  • Matplotlib automatically determines the x and y coordinates based on the array's indices
  • X and Y parameters
    • The coordinates of the values in Z
    • X and Y must both be 2D arrays with the same shape as Z
    • x1 is used for X containing x1 values
    • x2 is used for Y containing x2 values
  • Z parameter
    • The height values over which the contour is drawn
    • ravel function from the NumPy library is used to flatten a multidimensional array into a one-dimensional array
      • x1 and x2 are flatten into a 1D array via the ravel function
      • They are then combined via the array function from the NumPy library into a 2D array
      • The result is then reshaped via the reshape function to match the shape of x1
    • Since the values of the reshaped 2D array are not feature scaled, the values are feature scaled via the transform method on the sc object
  • alpha parameter
    • The alpha blending value, between 0 (transparent) and 1 (opaque)
    • Value of 0.75 is used to make the blending mostly opaque
  • cmap parameter
    • The Colormap object instance or registered colormap name used to map scalar data to colors
    • salmon and dodgerblue are used for a ListedColormap object
      • salmon = 0 or negative classifier
      • dodgerblue = 1 or positive classifier
• xlim function from the Matplotlib library is used to get or set the x-axis limits of the current axes
  • min() and max() for x1 are used for the limits
• ylim function from the Matplotlib library is used to get or set the y-axis limits of the current axes
  • min() and max() for x2 are used for the limits
• The values from y_set are iterated over in a for-in loop
  • unique function from the NumPy library returns sorted, unique elements of an array
    • Values of y_set are made unique and sorted
  • Iterator variable i represents the current row of iteration
  • Iterator variable j represents the classification value for the dependent variable
    • 0 negative classifier
    • 1 positive classifier
• scatter method from the Matplotlib library creates a scatter plot of data points with the shaded contour showing the classification for the dependent variable
  • x-axis uses values from x_set where y_set value = 0 (negative classifier)
  • y-axis uses values from x_set where y_set value = 1 (positive classifier)
  • c parameter
    • The marker colors
    • Uses the ListedColormap with the classification colors for the current row at index i
  • label parameter
    • Sets the label
    • Values
      • 0 negative classifier
      • 1 positive classifier

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Development

Python Virtual Environment

Create Python virtual environment:

cd ~/workspace/opengood-aio/py-ml-plot/.venv
python3 -m venv ~/workspace/opengood-aio/py-ml-plot/.venv
source .venv/bin/activate

Install Packages

python3 -m pip install matplotlib
python3 -m pip install numpy
python3 -m pip install pandas
python3 -m pip install scikit-learn

Create Requirements File

pip freeze > requirements.txt

Run Tests

python -m pytest tests/