# coding: utf-8
# # Logistic Regression With Linear Boundary Demo
#
# _Source: 🤖[Homemade Machine Learning](https://github.com/trekhleb/homemade-machine-learning) repository_
#
# > ☝Before moving on with this demo you might want to take a look at:
# > - 📗[Math behind the Logistic Regression](https://github.com/trekhleb/homemade-machine-learning/tree/master/homemade/logistic_regression)
# > - ⚙️[Logistic Regression Source Code](https://github.com/trekhleb/homemade-machine-learning/blob/master/homemade/logistic_regression/logistic_regression.py)
#
# **Logistic regression** is the appropriate regression analysis to conduct when the dependent variable is dichotomous (binary). Like all regression analyses, the logistic regression is a predictive analysis. Logistic regression is used to describe data and to explain the relationship between one dependent binary variable and one or more nominal, ordinal, interval or ratio-level independent variables.
#
# Logistic Regression is used when the dependent variable (target) is categorical.
#
# For example:
#
# - To predict whether an email is spam (`1`) or (`0`).
# - Whether online transaction is fraudulent (`1`) or not (`0`).
# - Whether the tumor is malignant (`1`) or not (`0`).
#
# > **Demo Project:** In this example we will try to classify Iris flowers into tree categories (`Iris setosa`, `Iris virginica` and `Iris versicolor`) based on `petal_length` and `petal_width` parameters.
# In[1]:
# To make debugging of logistic_regression module easier we enable imported modules autoreloading feature.
# By doing this you may change the code of logistic_regression library and all these changes will be available here.
get_ipython().run_line_magic('load_ext', 'autoreload')
get_ipython().run_line_magic('autoreload', '2')
# Add project root folder to module loading paths.
import sys
sys.path.append('../..')
# ### Import Dependencies
#
# - [pandas](https://pandas.pydata.org/) - library that we will use for loading and displaying the data in a table
# - [numpy](http://www.numpy.org/) - library that we will use for linear algebra operations
# - [matplotlib](https://matplotlib.org/) - library that we will use for plotting the data
# - [logistic_regression](https://github.com/trekhleb/homemade-machine-learning/blob/master/homemade/logistic_regression/logistic_regression.py) - custom implementation of logistic regression
# In[2]:
# Import 3rd party dependencies.
import numpy as np
import pandas as pd
import matplotlib.pyplot as plt
# Import custom logistic regression implementation.
from homemade.logistic_regression import LogisticRegression
# ### Load the Data
#
# In this demo we will use [Iris data set](http://archive.ics.uci.edu/ml/datasets/Iris).
#
# The data set consists of several samples from each of three species of Iris (`Iris setosa`, `Iris virginica` and `Iris versicolor`). Four features were measured from each sample: the length and the width of the sepals and petals, in centimeters. Based on the combination of these four features, [Ronald Fisher](https://en.wikipedia.org/wiki/Iris_flower_data_set) developed a linear discriminant model to distinguish the species from each other.
# In[3]:
# Load the data.
data = pd.read_csv('../../data/iris.csv')
# Print the data table.
data.head(10)
# ### Plot the Data
#
# Let's take two parameters `petal_length` and `petal_width` for each flower into consideration and plot the dependency of the Iris class on these two parameters.
# In[4]:
# List of suppported Iris classes.
iris_types = ['SETOSA', 'VERSICOLOR', 'VIRGINICA']
# Pick the Iris parameters for consideration.
x_axis = 'petal_length'
y_axis = 'petal_width'
# Plot the scatter for every type of Iris.
for iris_type in iris_types:
plt.scatter(
data[x_axis][data['class'] == iris_type],
data[y_axis][data['class'] == iris_type],
label=iris_type
)
# Plot the data.
plt.xlabel(x_axis + ' (cm)')
plt.ylabel(y_axis + ' (cm)')
plt.title('Iris Types')
plt.legend()
plt.show()
# ### Prepara the Data for Training
#
# Let's extract `petal_length` and `petal_width` data and form a training feature set and let's also form out training labels set.
# In[5]:
# Get total number of Iris examples.
num_examples = data.shape[0]
# Get features.
x_train = data[[x_axis, y_axis]].values.reshape((num_examples, 2))
# Get labels.
y_train = data['class'].values.reshape((num_examples, 1))
# ### Init and Train Logistic Regression Model
#
# > ☝🏻This is the place where you might want to play with model configuration.
#
# - `polynomial_degree` - this parameter will allow you to add additional polynomial features of certain degree. More features - more curved the line will be.
# - `max_iterations` - this is the maximum number of iterations that gradient descent algorithm will use to find the minimum of a cost function. Low numbers may prevent gradient descent from reaching the minimum. High numbers will make the algorithm work longer without improving its accuracy.
# - `regularization_param` - parameter that will fight overfitting. The higher the parameter, the simplier is the model will be.
# - `polynomial_degree` - the degree of additional polynomial features (`x1^2 * x2, x1^2 * x2^2, ...`). This will allow you to curve the predictions.
# - `sinusoid_degree` - the degree of sinusoid parameter multipliers of additional features (`sin(x), sin(2*x), ...`). This will allow you to curve the predictions by adding sinusoidal component to the prediction curve.
# In[6]:
# Set up linear regression parameters.
max_iterations = 1000 # Max number of gradient descent iterations.
regularization_param = 0 # Helps to fight model overfitting.
polynomial_degree = 0 # The degree of additional polynomial features.
sinusoid_degree = 0 # The degree of sinusoid parameter multipliers of additional features.
# Init logistic regression instance.
logistic_regression = LogisticRegression(x_train, y_train, polynomial_degree, sinusoid_degree)
# Train logistic regression.
(thetas, costs) = logistic_regression.train(regularization_param, max_iterations)
# Print model parameters that have been learned.
pd.DataFrame(thetas, columns=['Theta 1', 'Theta 2', 'Theta 3'], index=['SETOSA', 'VERSICOLOR', 'VIRGINICA'])
# ### Analyze Gradient Descent Progress
#
# The plot below illustrates how the cost function value changes over each iteration. You should see it decreasing.
#
# In case if cost function value increases it may mean that gradient descent missed the cost function minimum and with each step it goes further away from it.
#
# From this plot you may also get an understanding of how many iterations you need to get an optimal value of the cost function.
# In[7]:
# Draw gradient descent progress for each label.
labels = logistic_regression.unique_labels
plt.plot(range(len(costs[0])), costs[0], label=labels[0])
plt.plot(range(len(costs[1])), costs[1], label=labels[1])
plt.plot(range(len(costs[2])), costs[2], label=labels[2])
plt.xlabel('Gradient Steps')
plt.ylabel('Cost')
plt.legend()
plt.show()
# ### Calculate Model Training Precision
#
# Calculate how many flowers from the training set have been guessed correctly.
# In[8]:
# Make training set predictions.
y_train_predictions = logistic_regression.predict(x_train)
# Check what percentage of them are actually correct.
precision = np.sum(y_train_predictions == y_train) / y_train.shape[0] * 100
print('Precision: {:5.4f}%'.format(precision))
# ### Draw Decision Boundaries
#
# Let's build our decision boundaries. These are the lines that distinguish classes from each other. This will give us a pretty clear overview of how successfull our training process was. You should see clear distinguishment of three sectors on the data plain.
# In[9]:
# Get the number of training examples.
num_examples = x_train.shape[0]
# Set up how many calculations we want to do along every axis.
samples = 150
# Generate test ranges for x and y axis.
x_min = np.min(x_train[:, 0])
x_max = np.max(x_train[:, 0])
y_min = np.min(x_train[:, 1])
y_max = np.max(x_train[:, 1])
X = np.linspace(x_min, x_max, samples)
Y = np.linspace(y_min, y_max, samples)
# z axis will contain our predictions. So let's get predictions for every pair of x and y.
Z_setosa = np.zeros((samples, samples))
Z_versicolor = np.zeros((samples, samples))
Z_virginica = np.zeros((samples, samples))
for x_index, x in enumerate(X):
for y_index, y in enumerate(Y):
data = np.array([[x, y]])
prediction = logistic_regression.predict(data)[0][0]
if prediction == 'SETOSA':
Z_setosa[x_index][y_index] = 1
elif prediction == 'VERSICOLOR':
Z_versicolor[x_index][y_index] = 1
elif prediction == 'VIRGINICA':
Z_virginica[x_index][y_index] = 1
# Now, when we have x, y and z axes being setup and calculated we may print decision boundaries.
for iris_type in iris_types:
plt.scatter(
x_train[(y_train == iris_type).flatten(), 0],
x_train[(y_train == iris_type).flatten(), 1],
label=iris_type
)
plt.contour(X, Y, Z_setosa)
plt.contour(X, Y, Z_versicolor)
plt.contour(X, Y, Z_virginica)
plt.xlabel(x_axis + ' (cm)')
plt.ylabel(y_axis + ' (cm)')
plt.title('Iris Types')
plt.legend()
plt.show()