I am trying to match the accuracy of a model.predict call to the final val_accuracy of model.fit(). I am using tf dataset.

val_ds = tf.keras.utils.image_dataset_from_directory( 'my_path', validation_split=0.2, subset="validation", seed=38, image_size=(SIZE,SIZE), )

The dataset setup for train_ds is similar. I prefetch both…

train_ds = train_ds.prefetch(buffer_size=AUTOTUNE) val_ds = val_ds.prefetch(buffer_size=AUTOTUNE)

Than I get the labels for the val_ds so I can use them later

true_categories = tf.concat([y for x, y in val_ds], axis=0)

My model

inputs = tf.keras.Input(shape=(SIZE, SIZE, 3)) # ... some other layers outputs = tf.keras.layers.Dense( len(CLASS_NAMES), activation = tf.keras.activations.softmax)(intermediate) model = tf.keras.Model(inputs, outputs)

Compiles fine

model.compile( optimizer = 'adam', loss=tf.keras.losses.SparseCategoricalCrossentropy(), metrics = ['accuracy'])

Seems to fit fine

history = model.fit( train_ds, validation_data=val_ds, epochs=10, class_weight=class_weights) #i do weight the classes due to imbalance

The last epoch output

Epoch 10: val_accuracy did not improve from 0.92291 176/176 [==============================] – 191s 1s/step – loss: 0.9876 – accuracy: 0.7318 – val_loss: 0.4650 – val_accuracy: 0.8580

Now I want to verify the val_accuracy == 0.8580 when I run model.predict()

predictions = model.predict(val_ds, verbose=2 ) flattened_predictions = predictions.argmax(axis=1) accuracy = metrics.accuracy_score(true_categories, flattened_predictions) print ("Accuracy = ", accuracy)

Accuracy = 0.7980014275517487

I would have expected that to equal the last val accuracy, which was 0.8580, but it is off. My val_ds uses a seed so I should be getting the images in the same order when I shuffle, right? Getting ground truth labels is a pain using datasets, but I think (???) my method is correct.

I only have two classes and when I look at my predictions variable it looks like I am getting probabilities as I would expect, so I think I set up, compiled and fit my model correctly for sparse categorical cross entropy using softmax on my final layer output.

predictions[:3] #show the first 3 predictions, the values sum to 1.0 as expected

array([[0.42447385, 0.5755262 ], [0.2162129 , 0.7837871 ], [0.31917858, 0.6808214 ]], dtype=float32)

What am I missing?

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## Answer

What you are missing is that your validation dataset is shuffled at every iteration.

`tf.keras.utils.image_dataset_from_directory`

has `shuffle=True`

by default. And that `shuffle`

method for a TensorFlow dataset has an argument `reshuffle_each_iteration`

which is `None`

by default. Therefore it is shuffled everytime.

The `seed=38`

parameter is used for tracking the samples that reserved for training and validation separately. In other words, with `seed`

argument we can follow which samples will be used for validation dataset and vice versa.

As an example:

dataset = tf.data.Dataset.range(6) dataset = dataset.shuffle(6, reshuffle_each_iteration=None, seed=154).batch(2) print("First time iteration:") for x in dataset: print(x) print("n") print("Second time iteration") for x in dataset: print(x)

This will print:

First time iteration: tf.Tensor([2 1], shape=(2,), dtype=int64) tf.Tensor([3 0], shape=(2,), dtype=int64) tf.Tensor([5 4], shape=(2,), dtype=int64) Second time iteration tf.Tensor([4 3], shape=(2,), dtype=int64) tf.Tensor([0 5], shape=(2,), dtype=int64) tf.Tensor([2 1], shape=(2,), dtype=int64)

Relevant source code for `tf.keras.utils.image_dataset_from_directory`

can be found here.

If you want to match predictions with their respective labels, then you can loop over the dataset:

predictions = [] labels = [] for x, y in val_ds: predictions.append(np.argmax(model(x), axis=-1)) labels.append(y.numpy()) predictions = np.concatenate(predictions, axis=0) labels = np.concatenate(labels, axis=0)

Then you can check accuracy.

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