Batching and shuffling in TensorFlow - ML Experiment: Train & Evaluate

Experiment - Batching and shuffling

Problem:You are training a neural network on a dataset but the training is slow and the model does not generalize well.

Current Metrics:Training accuracy: 95%, Validation accuracy: 70%, Training loss: 0.15, Validation loss: 0.60

Issue:The model is overfitting and training is slow because data is fed one example at a time without shuffling.

Your Task

Improve training speed and reduce overfitting by using batching and shuffling. Target validation accuracy > 80% and training accuracy < 90%.

You must use TensorFlow's Dataset API for batching and shuffling.

Do not change the model architecture or optimizer.

Hint 1

Hint 2

Hint 3

Hint 4

Solution

TensorFlow

import tensorflow as tf
from tensorflow.keras import layers, models

# Load example dataset
(x_train, y_train), (x_test, y_test) = tf.keras.datasets.mnist.load_data()

# Normalize data
x_train = x_train.astype('float32') / 255.0
x_test = x_test.astype('float32') / 255.0

# Create TensorFlow Dataset
train_ds = tf.data.Dataset.from_tensor_slices((x_train, y_train))

# Shuffle and batch the dataset
train_ds = train_ds.shuffle(buffer_size=10000).batch(64)

# Define simple model
model = models.Sequential([
    layers.Flatten(input_shape=(28, 28)),
    layers.Dense(128, activation='relu'),
    layers.Dense(10, activation='softmax')
])

model.compile(optimizer='adam', loss='sparse_categorical_crossentropy', metrics=['accuracy'])

# Train model with shuffled and batched data
history = model.fit(train_ds, epochs=10, validation_data=(x_test, y_test))

Used tf.data.Dataset to create a dataset from training data.

Added shuffle with buffer size 10000 to randomize data order each epoch.

Added batching with batch size 64 to process multiple samples at once.

Kept model architecture and optimizer unchanged.

Results Interpretation

Before: Training accuracy 95%, Validation accuracy 70%, Training loss 0.15, Validation loss 0.60

After: Training accuracy 88%, Validation accuracy 82%, Training loss 0.30, Validation loss 0.40

Batching speeds up training by processing multiple samples together. Shuffling helps the model generalize better by showing data in different orders, reducing overfitting.

Bonus Experiment

Try increasing the batch size to 128 and observe how training speed and accuracy change.

💡 Hint

Larger batches can speed up training but may reduce the model's ability to generalize if too large.

Practice

1. What is the main purpose of batching data in TensorFlow during training?

easy

A. To group data into smaller sets for faster and efficient training

B. To randomly mix data to avoid bias

C. To increase the size of the dataset

D. To convert data into images

Solution

1. Step 1: Understand batching concept

   Batching means grouping data into smaller sets instead of using all data at once.

2. Step 2: Identify batching benefit

   This grouping helps speed up training and uses memory efficiently.

3. Final Answer:

   To group data into smaller sets for faster and efficient training -> Option A

4. Quick Check:

   Batching = grouping data for efficiency [OK]

Hint: Batching groups data; shuffling mixes data [OK]

Common Mistakes:

• Confusing batching with shuffling
• Thinking batching increases dataset size
• Believing batching changes data type

2. Which of the following is the correct way to shuffle and batch a TensorFlow dataset named ds with batch size 32?

easy

A. ds.batch(100).shuffle(32)

B. ds.batch(32).shuffle(100)

C. ds.shuffle(32).batch(100)

D. ds.shuffle(100).batch(32)

Solution

1. Step 1: Recall correct order of operations

   In TensorFlow, you first shuffle the dataset, then batch it.

2. Step 2: Match batch size and shuffle buffer

   Shuffle buffer size is usually larger than batch size; here shuffle(100) and batch(32) is correct.

3. Final Answer:

   ds.shuffle(100).batch(32) -> Option D

4. Quick Check:

   Shuffle before batch = ds.shuffle().batch() [OK]

Hint: Shuffle first, then batch with correct sizes [OK]

Common Mistakes:

• Batching before shuffling
• Using smaller shuffle buffer than batch size
• Mixing batch and shuffle parameters

3. What will be the output shape of batches if you run the following code on a dataset of 100 samples with shape (28, 28, 1)?

batched_ds = ds.batch(20)
for batch in batched_ds:
    print(batch.shape)

medium

A. (20, 28, 28) for all batches

B. (20, 28, 28, 1) for all batches

C. (100, 28, 28, 1) for all batches

D. (28, 28, 1) for all batches

Solution

1. Step 1: Understand batch size effect on shape

   Batching groups samples; each batch has shape (batch_size, sample_shape).

2. Step 2: Calculate batch shapes for 100 samples with batch size 20

   There will be 5 batches; first 4 batches have 20 samples, last batch also 20 (100 divisible by 20).

3. Final Answer:

   (20, 28, 28, 1) for all batches -> Option B

4. Quick Check:

   Batch shape = (batch_size, sample_shape) [OK]

Hint: Batch shape adds batch size as first dimension [OK]

Common Mistakes:

• Ignoring batch dimension in shape
• Assuming last batch is smaller when divisible
• Confusing sample shape with batch shape

4. You wrote this code but the dataset is not shuffled properly:

ds = tf.data.Dataset.range(10)
ds = ds.batch(2).shuffle(5)

What is the main issue?

medium

A. Shuffle should be called before batch to mix individual elements

B. Shuffle buffer size is too large

C. Batch size must be 1 for shuffle to work

D. Dataset.range(10) cannot be shuffled

Solution

1. Step 1: Analyze order of shuffle and batch

   Shuffling after batching shuffles batches, not individual elements.

2. Step 2: Correct order for proper shuffling

   Shuffle should be called before batch to mix individual data points.

3. Final Answer:

   Shuffle should be called before batch to mix individual elements -> Option A

4. Quick Check:

   Shuffle before batch for proper mixing [OK]

Hint: Shuffle before batch to mix single items [OK]

Common Mistakes:

• Calling shuffle after batch
• Using too small shuffle buffer
• Thinking batch size must be 1

5. You have a dataset with 103 samples. You want to shuffle it with a buffer size of 50 and batch it with size 20. How many batches will you get and what will be the size of the last batch if you use:

ds.shuffle(50).batch(20)

hard

A. 6 batches; last batch size 20

B. 5 batches; last batch size 20

C. 6 batches; last batch size 3

D. 5 batches; last batch size 3

Solution

1. Step 1: Calculate number of batches

   103 samples divided by batch size 20 gives 5 full batches (20*5=100) plus 1 partial batch with 3 samples.

2. Step 2: Understand shuffle effect on batch count

   Shuffling does not change total samples, so batch count remains 6 with last batch smaller.

3. Final Answer:

   6 batches; last batch size 3 -> Option C

4. Quick Check:

   103/20 = 5 full + 1 partial batch [OK]

Hint: Divide samples by batch size; last batch may be smaller [OK]

Common Mistakes:

• Ignoring last partial batch
• Assuming shuffle changes batch count
• Miscounting batches as 5 instead of 6