ANN Classification with 'nnet' Package in Rust
Published: 2023-01-17 09:26:13

Artificial neural networks (ANNs) are machine learning algorithms that are inspired by the structure and function of the human brain. They are used for tasks such as image classification, language translation, and prediction. In the programming language R, the nnet package can be used to train and use ANNs for classification tasks.

**Concepts**

Before diving into the nnet package, it is helpful to understand some key concepts related to ANNs and classification.

- **Neurons:** The basic unit of an ANN is a neuron, which receives input from other neurons or from external data and produces an output.
- **Layers:** Neurons are organized into layers, with the input layer receiving data and the output layer producing the final output. There may also be hidden layers between the input and output layers.
- **Weights:** Each connection between neurons has an associated weight, which determines the strength of the connection. These weights are adjusted during training to optimize the performance of the ANN.
- **Activation function:** The activation function of a neuron determines how the input is transformed into an output. Common activation functions include sigmoid, tanh, and ReLU.
-** Classification:** Classification is a type of machine learning task in which the goal is to predict a categorical label for a given input. For example, an ANN might be trained to classify images as either "cat" or "dog."
 

**Steps**

To use the nnet package for classification in R, you will need to follow these steps:

1. - Load the nnet package using library(nnet).
2. - Prepare your data. This typically involves dividing it into training and test sets, and possibly scaling or preprocessing the data in some way.
3. - Train the ANN using the nnet function. You will need to specify the number of hidden layers and the number of neurons in each layer, as well as the activation function and the number of epochs (iterations over the training data).
4. - Use the trained ANN to make predictions on new data using the predict function.

Examples

Here is an example of using the nnet package to train an ANN for binary classification using the iris dataset:

```
# Load the nnet package and the iris dataset
library(nnet)
data(iris)

# Divide the data into training and test sets
set.seed(123)
indices <- sample(1:nrow(iris), size = 0.8 * nrow(iris))
train <- iris[indices,]
test <- iris[-indices,]

# Train the ANN
model <- nnet(Species ~ ., data = train, size = 4, decay = 5e-4, maxit = 200)

# Make predictions on the test set
predictions <- predict(model, test[,-5])

# Calculate the accuracy of the predictions
accuracy <- mean(predictions == test[,5])
print(accuracy)

```
This code will output the accuracy of the ANN's predictions on the test set, which will be a value between 0 and 1.

You can also use the nnet package for multi-class classification by setting the softmax = TRUE option in the nnet function and using the multinom function for predictions.

In this example, we have used a relatively simple dataset with only four input features. For more complex datasets, you may need to use a deeper or wider ANN, or consider using other techniques such as regularization or early stopping to improve the performance of your model. You may also want to experiment with different activation functions and learning rates to find the best combination for your specific task.

It is also important to keep in mind that ANNs can be sensitive to the initialization of the weights and may produce different results each time they are trained, even on the same dataset. To mitigate this issue, you may want to train your ANN multiple times with different random seeds and choose the one with the best performance.

Here is an another example of how to use Rust to train an ANN for classification using the nnet package :

First, you will need to install the nnet package and its dependencies. Then, you can use the Train and Predict functions provided by the package to train and use the ANN.

Here is some example code that demonstrates how to train and use an ANN for binary classification using the iris dataset in Rust

```
extern crate nnet;
extern crate rand;

use nnet::{Activation, Layer, Network, Trainer, TrainingError};
use rand::Rng;

fn main() -> Result<(), TrainingError> {
    // Load the iris dataset
    let data = nnet::datasets::iris::load()?;

    // Divide the data into training and test sets
    let mut rng = rand::thread_rng();
    let mut data = data.shuffle(&mut rng);
    let train_size = (data.len() as f64 * 0.8) as usize;
    let (train_data, test_data) = data.split_at(train_size);

    // Convert the Species column to a binary variable
    let train_data: Vec<_> = train_data
        .iter()
        .map(|row| {
            let species = if row[4] == "setosa" { 0.0 } else { 1.0 };
            [row[0], row[1], row[2], row[3], species]
        })
        .collect();
    let test_data: Vec<_> = test_data
        .iter()
        .map(|row| {
            let species = if row[4] == "setosa" { 0.0 } else { 1.0 };
            [row[0], row[1], row[2], row[3], species]
        })
        .collect();

    // Create the ANN
    let mut net = Network::new(&[
        Layer::new(4, Activation::Sigmoid),
        Layer::new(4, Activation::Sigmoid),
        Layer::new(1, Activation::Sigmoid),
    ]);

    // Train the ANN
    let mut trainer = Trainer::new(&mut net);
    trainer.train(&train_data, 200, |_, _| 0.1)?;

    // Make predictions on the test set
    let mut correct = 0;
    for row in test_data {
        let inputs = &row[0..4];
        let target = row[4];
        let output = net.predict(inputs);
        if (output[0] - target).abs() < 0.5 {
            correct += 1;
        }
    }

    // Calculate the accuracy of the predictions
    let accuracy = correct as f64 / test_data.len() as f64;
    println!("Accuracy: {}", accuracy);

    Ok(())
}

```
This code will output the accuracy of the ANN's predictions on the test set, which will be a value between 0 and 1. This model will be trained to predict whether a given iris is a setosa or non-setosa species based on its sepal length, sepal width, petal length, and petal width. The training and test sets are created by shuffling the data and then splitting it into 80% and 20% of the total data, respectively. The species are then converted to binary values of 0 and 1.

The ANN is created with three layers, with the first and second layers having four neurons and using a sigmoid activation function, and the third layer having one neuron and using a sigmoid activation function. The ANN is then trained using 200 epochs and a learning rate of 0.1.

Finally, the trained ANN is used to make predictions on the test set and the accuracy is calculated by comparing the predictions to the actual species values. The accuracy is then printed to the console.

I hope this example helps to demonstrate how to use the nnet package in Rust to train and use an ANN for classification tasks. Please let me know if you have any further questions.

In conclusion, the nnet package in R provides a simple and effective way to implement and use ANNs for classification tasks. With a little experimentation and fine-tuning, you can achieve good performance on a variety of datasets.