Expectation–Maximization (EM) algorithm

 

Expt No: 10                                           Expectation–Maximization (EM) algorithm

Date:

 

Aim: To write a program to demonstrate how missing values are handled using SimpleImputer and Expectation–Maximization (EM) algorithms

 

Program

# SimpleImputer method

 

import pandas as pd

from sklearn.model_selection import train_test_split

from sklearn.naive_bayes import GaussianNB

from sklearn.metrics import accuracy_score

from sklearn.impute import SimpleImputer

 

# Step 1: Load the dataset with missing values

iris_data = pd.read_csv("Iris.csv")

 

# Step 2: Introduce missing values in a specific feature (e.g., Petal length)

feature_with_missing_values = "PetalLength"

missing_percentage = 0.2

 

# Randomly select indices to introduce missing values

missing_indices = iris_data.sample(frac=missing_percentage, random_state=42).index

 

# Set the selected indices to NaN in the chosen feature

iris_data.loc[missing_indices, feature_with_missing_values] = None

 

# Step 3: Define features and target

X = iris_data.drop("Species", axis=1)

y = iris_data["Species"]

 

# Step 4: Split the dataset into train and test sets

X_train, X_test, y_train, y_test = train_test_split(X, y, test_size=0.2, random_state=42)

 

# Step 5: Preprocess the data to handle missing values

imputer = SimpleImputer(strategy="mean")

X_train_imputed = imputer.fit_transform(X_train)

X_test_imputed = imputer.transform(X_test)

 

# Step 6: Train a Naive Bayes classifier

classifier = GaussianNB()

classifier.fit(X_train_imputed, y_train)

 

# Step 7: Make predictions

y_pred = classifier.predict(X_test_imputed)

 

# Step 8: Calculate accuracy

accuracy = accuracy_score(y_test, y_pred)

print("Accuracy after imputing missing values with SimpleImputer: {:.4f}".format(accuracy))

 

 

# EM Algorithm

import pandas as pd

from sklearn.model_selection import train_test_split

from sklearn.naive_bayes import GaussianNB

from sklearn.metrics import accuracy_score

from sklearn.mixture import GaussianMixture

import os

import warnings

 

os.environ["OMP_NUM_THREADS"] = "1"

warnings.filterwarnings("ignore", category=UserWarning)

 

# Step 1: Load the dataset with missing values

iris_data = pd.read_csv("Iris.csv")

 

# Step 2: Introduce missing values in a specific feature (e.g., PetalLength)

feature_with_missing_values = "PetalLength"

missing_percentage = 0.2

 

# Randomly select indices to introduce missing values

missing_indices = iris_data.sample(frac=missing_percentage, random_state=42).index

 

# Set the selected indices to NaN in the chosen feature

iris_data.loc[missing_indices, feature_with_missing_values] = None

 

# Step 3: Define features and target

X = iris_data.drop("Species", axis=1)

y = iris_data["Species"]

 

# Step 4: Split the dataset into train and test sets

X_train, X_test, y_train, y_test = train_test_split(X, y, test_size=0.2, random_state=42)

 

# Step 5: Initialize GMM

gmm = GaussianMixture(n_components=3, random_state=42)

 

# Step 6: Impute missing values using EM algorithm

X_train_imputed = X_train.copy()

X_test_imputed = X_test.copy()

 

for feature in X_train_imputed.columns:

    missing_train_indices = X_train_imputed[X_train_imputed[feature].isnull()].index

    missing_test_indices = X_test_imputed[X_test_imputed[feature].isnull()].index

   

    # Fit GMM on non-missing values

    gmm.fit(X_train_imputed.loc[~X_train_imputed.index.isin(missing_train_indices), [feature]])

   

    # Impute missing values using GMM

    n_samples_train = max(len(missing_train_indices), 1)

    n_samples_test = max(len(missing_test_indices), 1)

   

    X_train_imputed.loc[missing_train_indices, [feature]] = gmm.sample(n_samples=n_samples_train)[0]

    X_test_imputed.loc[missing_test_indices, [feature]] = gmm.sample(n_samples=n_samples_test)[0]

 

# Step 7: Train a Naive Bayes classifier

classifier = GaussianNB()

classifier.fit(X_train_imputed, y_train)

 

# Step 8: Make predictions

y_pred = classifier.predict(X_test_imputed)

 

# Step 9: Calculate accuracy

accuracy = accuracy_score(y_test, y_pred)

print("Accuracy after imputing missing values with EM algorithm: {:.4f}".format(accuracy))

 

 

Result: Thus the program to demonstrate ________________ was written and executed.

Sample Output

 

# SimpleImputer method

Accuracy after imputing missing values with SimpleImputer: 0.6333

 

# EM Algorithm

Accuracy after imputing missing values with EM algorithm: 0.7667