# Example 5: Image Classification using Data Generator

This example uses the image data generator `tensorflow.keras.preprocessing.image.ImageDataGenerator` to feed data to the model. Instead of reading all the data in the memory, the data generator generates the data needed by the model and only save it in the memory instead of saving all the data. This frees the memory but adds more computational time. 

```python
import tensorflow as tf
import tensorflow.keras
import pygad.kerasga
import pygad

def fitness_func(ga_instanse, solution, sol_idx):
    global train_generator, data_outputs, keras_ga, model

    predictions = pygad.kerasga.predict(model=model,
                                        solution=solution,
                                        data=train_generator)

    cce = tensorflow.keras.losses.CategoricalCrossentropy()
    solution_fitness = 1.0 / (cce(data_outputs, predictions).numpy() + 0.00000001)

    return solution_fitness

def on_generation(ga_instance):
    print("Generation = {ga_instance.generations_completed}")
    print("Fitness    = {ga_instance.best_solution(ga_instance.last_generation_fitness)[1]}")

# The dataset path.
dataset_path = r'../data/Skin_Cancer_Dataset' 

num_classes = 2
img_size = 224

# Create a simple CNN. This does not gurantee high classification accuracy.
model = tf.keras.models.Sequential()
model.add(tf.keras.layers.Input(shape=(img_size, img_size, 3)))
model.add(tf.keras.layers.Conv2D(32, (3,3), activation="relu", padding="same"))
model.add(tf.keras.layers.MaxPooling2D((2, 2)))
model.add(tf.keras.layers.Flatten())
model.add(tf.keras.layers.Dropout(rate=0.2))
model.add(tf.keras.layers.Dense(num_classes, activation="softmax"))

# Create an instance of the pygad.kerasga.KerasGA class to build the initial population.
keras_ga = pygad.kerasga.KerasGA(model=model,
                                 num_solutions=10)

data_generator = tf.keras.preprocessing.image.ImageDataGenerator()
train_generator = data_generator.flow_from_directory(dataset_path, 
                                                     class_mode='categorical',
                                                     target_size=(224, 224),
                                                     batch_size=32,
                                                     shuffle=False)
# train_generator.class_indices
data_outputs = tf.keras.utils.to_categorical(train_generator.labels)

# Check the documentation for more information about the parameters: https://pygad.readthedocs.io/en/latest/pygad.html#pygad-ga-class
initial_population = keras_ga.population_weights # Initial population of network weights.

# Create an instance of the pygad.GA class
ga_instance = pygad.GA(num_generations=10, 
                       num_parents_mating=5, 
                       initial_population=initial_population,
                       fitness_func=fitness_func,
                       on_generation=on_generation)

# Start the genetic algorithm evolution.
ga_instance.run()

# After the generations complete, a plot is shown that summarizes how the fitness values evolve over the generations.
ga_instance.plot_fitness(title="PyGAD & Keras - Iteration vs. Fitness", linewidth=4)

# Returning the details of the best solution.
solution, solution_fitness, solution_idx = ga_instance.best_solution(ga_instance.last_generation_fitness)
print(f"Fitness value of the best solution = {solution_fitness}")
print(f"Index of the best solution : {solution_idx}")

predictions = pygad.kerasga.predict(model=model,
                                    solution=solution,
                                    data=train_generator)
# print(f"Predictions : \n{predictions}")

# Calculate the categorical crossentropy for the trained model.
cce = tensorflow.keras.losses.CategoricalCrossentropy()
print(f"Categorical Crossentropy : {cce(data_outputs, predictions).numpy()}")

# Calculate the classification accuracy for the trained model.
ca = tensorflow.keras.metrics.CategoricalAccuracy()
ca.update_state(data_outputs, predictions)
accuracy = ca.result().numpy()
print(f"Accuracy : {accuracy}")
```