[PYTHON] Difference between "categorical_crossentropy" and "sparse_categorical_crossentropy"


--The label used is different. That's the only difference. For "categorical_crossentropy", use the label onehot (somewhere is 1 and all others are 0). Use an integer for the label "sparse_categorical_crossentropy".

Difference between one-hot and integer representation

Example) In the case of 10 classifications

one-hot expression Integer representation
[0. 0. 0. 0. 0. 0. 0. 0. 0. 1.] [9]
[0. 0. 1. 0. 0. 0. 0. 0. 0. 0.] [2]
[0. 1. 0. 0. 0. 0. 0. 0. 0. 0.] [1]
[0. 0. 0. 0. 0. 1. 0. 0. 0. 0.] [5]

Convert integer labels to one-hot labels

I get the impression that many datasets have integer labels, but many loss functions do not work unless you give them one-hot labels instead of integer labels. In such a case, you need to convert. (Rather, I feel that there are a minority of loss functions that can be learned with integer labels, such as "sparse_categorical_crossentropy".)

The code is shown below.

import numpy as np

n_labels = len(np.unique(train_labels))
train_labels_onehot = np.eye(n_labels)[train_labels]

n_labels = len(np.unique(test_labels))
test_labels_onehot = np.eye(n_labels)[test_labels]

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