feat: add Perceptron algorithm in machine learning (#1000)

Author: Dcyaprogrammer

DIRECTORY.md

@@ -209,6 +209,7 @@
     * [Linear Regression](https://github.com/TheAlgorithms/Rust/blob/master/src/machine_learning/linear_regression.rs)
     * [Logistic Regression](https://github.com/TheAlgorithms/Rust/blob/master/src/machine_learning/logistic_regression.rs)
     * [Naive Bayes](https://github.com/TheAlgorithms/Rust/blob/master/src/machine_learning/naive_bayes.rs)
+    * [Perceptron](https://github.com/TheAlgorithms/Rust/blob/master/src/machine_learning/perceptron.rs)
     * [Principal Component Analysis](https://github.com/TheAlgorithms/Rust/blob/master/src/machine_learning/principal_component_analysis.rs)
     * Loss Function
       * [Average Margin Ranking Loss](https://github.com/TheAlgorithms/Rust/blob/master/src/machine_learning/loss_function/average_margin_ranking_loss.rs)

src/machine_learning/mod.rs

@@ -6,6 +6,7 @@ mod logistic_regression;
 mod loss_function;
 mod naive_bayes;
 mod optimization;
+mod perceptron;
 mod principal_component_analysis;
 
 pub use self::cholesky::cholesky;
@@ -23,4 +24,6 @@ pub use self::loss_function::neg_log_likelihood;
 pub use self::naive_bayes::naive_bayes;
 pub use self::optimization::gradient_descent;
 pub use self::optimization::Adam;
+pub use self::perceptron::classify;
+pub use self::perceptron::perceptron;
 pub use self::principal_component_analysis::principal_component_analysis;

src/machine_learning/perceptron.rs

@@ -0,0 +1,231 @@
+/// Returns the weights and bias after performing Perceptron algorithm on the input data points.
+/// The Perceptron is a binary classification algorithm that learns a linear separator.
+/// Labels should be either -1.0 or 1.0 for the two classes.
+pub fn perceptron(
+    data_points: Vec<(Vec<f64>, f64)>,
+    max_iterations: usize,
+    learning_rate: f64,
+) -> Option<(Vec<f64>, f64)> {
+    if data_points.is_empty() {
+        return None;
+    }
+
+    let num_features = data_points[0].0.len();
+    if num_features == 0 {
+        return None;
+    }
+
+    let mut weights = vec![0.0; num_features];
+    let mut bias = 0.0;
+
+    for _ in 0..max_iterations {
+        let mut misclassified = 0;
+
+        for (features, label) in &data_points {
+            let prediction = predict(&weights, bias, features);
+
+            if prediction != *label {
+                misclassified += 1;
+
+                for (weight, feature) in weights.iter_mut().zip(features.iter()) {
+                    *weight += learning_rate * label * feature;
+                }
+                bias += learning_rate * label;
+            }
+        }
+
+        if misclassified == 0 {
+            break;
+        }
+    }
+
+    Some((weights, bias))
+}
+
+/// Make a prediction using the given weights and bias.
+fn predict(weights: &[f64], bias: f64, features: &[f64]) -> f64 {
+    let sum = weights
+        .iter()
+        .zip(features.iter())
+        .map(|(w, x)| w * x)
+        .sum::<f64>()
+        + bias;
+
+    if sum >= 0.0 {
+        1.0
+    } else {
+        -1.0
+    }
+}
+
+/// Classify a new data point using the learned weights and bias.
+pub fn classify(weights: &[f64], bias: f64, features: &[f64]) -> Option<f64> {
+    if weights.is_empty() || features.is_empty() {
+        return None;
+    }
+
+    if weights.len() != features.len() {
+        return None;
+    }
+
+    Some(predict(weights, bias, features))
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn test_perceptron_linearly_separable() {
+        let data = vec![
+            (vec![1.0, 1.0], 1.0),
+            (vec![2.0, 2.0], 1.0),
+            (vec![3.0, 3.0], 1.0),
+            (vec![-1.0, -1.0], -1.0),
+            (vec![-2.0, -2.0], -1.0),
+            (vec![-3.0, -3.0], -1.0),
+        ];
+
+        let result = perceptron(data, 100, 0.1);
+        assert!(result.is_some());
+
+        let (weights, bias) = result.unwrap();
+
+        let prediction1 = classify(&weights, bias, &[2.5, 2.5]);
+        assert_eq!(prediction1, Some(1.0));
+
+        let prediction2 = classify(&weights, bias, &[-2.5, -2.5]);
+        assert_eq!(prediction2, Some(-1.0));
+    }
+
+    #[test]
+    fn test_perceptron_xor_like() {
+        let data = vec![
+            (vec![0.0, 0.0], -1.0),
+            (vec![1.0, 1.0], 1.0),
+            (vec![0.0, 1.0], -1.0),
+            (vec![1.0, 0.0], -1.0),
+        ];
+
+        let result = perceptron(data, 100, 0.1);
+        assert!(result.is_some());
+
+        let (weights, _bias) = result.unwrap();
+        assert_eq!(weights.len(), 2);
+    }
+
+    #[test]
+    fn test_perceptron_single_feature() {
+        let data = vec![
+            (vec![1.0], 1.0),
+            (vec![2.0], 1.0),
+            (vec![3.0], 1.0),
+            (vec![-1.0], -1.0),
+            (vec![-2.0], -1.0),
+            (vec![-3.0], -1.0),
+        ];
+
+        let result = perceptron(data, 100, 0.1);
+        assert!(result.is_some());
+
+        let (weights, bias) = result.unwrap();
+        assert_eq!(weights.len(), 1);
+
+        let prediction1 = classify(&weights, bias, &[5.0]);
+        assert_eq!(prediction1, Some(1.0));
+
+        let prediction2 = classify(&weights, bias, &[-5.0]);
+        assert_eq!(prediction2, Some(-1.0));
+    }
+
+    #[test]
+    fn test_perceptron_empty_data() {
+        let result = perceptron(vec![], 100, 0.1);
+        assert_eq!(result, None);
+    }
+
+    #[test]
+    fn test_perceptron_empty_features() {
+        let data = vec![(vec![], 1.0), (vec![], -1.0)];
+        let result = perceptron(data, 100, 0.1);
+        assert_eq!(result, None);
+    }
+
+    #[test]
+    fn test_perceptron_zero_iterations() {
+        let data = vec![(vec![1.0, 1.0], 1.0), (vec![-1.0, -1.0], -1.0)];
+
+        let result = perceptron(data, 0, 0.1);
+        assert!(result.is_some());
+
+        let (weights, bias) = result.unwrap();
+        assert_eq!(weights, vec![0.0, 0.0]);
+        assert_eq!(bias, 0.0);
+    }
+
+    #[test]
+    fn test_classify_empty_weights() {
+        let result = classify(&[], 0.0, &[1.0, 2.0]);
+        assert_eq!(result, None);
+    }
+
+    #[test]
+    fn test_classify_empty_features() {
+        let result = classify(&[1.0, 2.0], 0.0, &[]);
+        assert_eq!(result, None);
+    }
+
+    #[test]
+    fn test_classify_mismatched_dimensions() {
+        let result = classify(&[1.0, 2.0], 0.0, &[1.0]);
+        assert_eq!(result, None);
+    }
+
+    #[test]
+    fn test_perceptron_different_learning_rates() {
+        let data = vec![
+            (vec![1.0, 1.0], 1.0),
+            (vec![2.0, 2.0], 1.0),
+            (vec![-1.0, -1.0], -1.0),
+            (vec![-2.0, -2.0], -1.0),
+        ];
+
+        let result1 = perceptron(data.clone(), 100, 0.01);
+        let result2 = perceptron(data, 100, 1.0);
+
+        assert!(result1.is_some());
+        assert!(result2.is_some());
+
+        let (weights1, bias1) = result1.unwrap();
+        let (weights2, bias2) = result2.unwrap();
+
+        let prediction1 = classify(&weights1, bias1, &[3.0, 3.0]);
+        let prediction2 = classify(&weights2, bias2, &[3.0, 3.0]);
+
+        assert_eq!(prediction1, Some(1.0));
+        assert_eq!(prediction2, Some(1.0));
+    }
+
+    #[test]
+    fn test_perceptron_with_bias() {
+        let data = vec![
+            (vec![1.0], 1.0),
+            (vec![2.0], 1.0),
+            (vec![10.0], 1.0),
+            (vec![0.0], -1.0),
+            (vec![-1.0], -1.0),
+            (vec![-10.0], -1.0),
+        ];
+
+        let result = perceptron(data, 100, 0.1);
+        assert!(result.is_some());
+
+        let (weights, bias) = result.unwrap();
+
+        let prediction_positive = classify(&weights, bias, &[5.0]);
+        let prediction_negative = classify(&weights, bias, &[-5.0]);
+
+        assert_eq!(prediction_positive, Some(1.0));
+        assert_eq!(prediction_negative, Some(-1.0));
+    }
+}