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How to Calculate Confusion Matrix on test Data?

I want to plot a confusion matrix on the validation data.

Specifically, I want to calculate a confusion matrix of the model output on the validation data.

I tried everything online, but couldn’t figure it out.

here is my model:

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

(train_images, train_labels), (test_images, test_labels) = datasets.cifar10.load_data()
train_images, test_images = train_images / 255.0, test_images / 255.0

model = models.Sequential()
# layers here

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

history = model.fit(train_images, train_labels, epochs=1, 
                    validation_data=(test_images, test_labels))

Answer

Here is a dummy example.

DataSet

(x_train, y_train), (x_test, y_test) = tf.keras.datasets.mnist.load_data()

# train set / data 
x_train = x_train.reshape(-1, 28*28)
x_train = x_train.astype('float32') / 255

# train set / target 
num_of_classess = 10 
y_train = tf.keras.utils.to_categorical(y_train , num_classes=num_of_classess )

Model

model = Sequential()
model.add(Dense(800, input_dim=784, activation="relu"))
model.add(Dense(num_of_classess , activation="softmax"))
model.compile(loss="categorical_crossentropy", optimizer="SGD", metrics=["accuracy"])
history = model.fit(x_train, y_train, 
                    batch_size=200, 
                    epochs=20,  
                    verbose=1)

Confusion Matrix

Your interest is mostly here.

# get predictions
y_pred = model.predict(x_train, verbose=2)

# compute confusion matrix with `tf` 
confusion = tf.math.confusion_matrix(
              labels = np.argmax(y_train, axis=1),      # get trule labels 
              predictions = np.argmax(y_pred, axis=1),  # get predicted labels 
              num_classes=num_of_classess)              # no. of classifier 

print(confusion)
<tf.Tensor: shape=(10, 10), dtype=int32, numpy=
array([[5750,    0,   16,   13,    9,   25,   40,    9,   54,    7],
       [   2, 6570,   28,   34,    8,   26,    6,   16,   45,    7],
       [  35,   44, 5425,   82,   93,   12,   69,   79,  100,   19],
       [  15,   24,  105, 5628,    4,  136,   26,   60,   82,   51],
       [   9,   29,   33,    6, 5483,    2,   60,   10,   33,  177],
       [  58,   32,   26,  159,   51, 4864,  101,   19,   67,   44],
       [  32,   18,   28,    3,   43,   60, 5697,    2,   33,    2],
       [  26,   46,   74,   19,   62,   10,    3, 5895,   15,  115],
       [  27,  101,   46,  142,   25,   71,   52,   15, 5304,   68],
       [  34,   30,   20,   94,  173,   21,    4,  162,   32, 5379]],
      dtype=int32)>

Visualization

Let’s visualize.

import seaborn as sns 
import pandas as pd 

cm = pd.DataFrame(confusion.numpy(), # use .numpy(), because now confusion is tensor
               range(num_of_classess),range(num_of_classess))

plt.figure(figsize = (10,10))
sns.heatmap(cm, annot=True, annot_kws={"size": 12}) # font size
plt.show()

enter image description here

Update

Based on the conversation, if you’ve to use

tf.keras.losses.SparseCategoricalCrossentropy(from_logits=True)

then don’t transform your integer label as I’ve shown you above (i.e. y_train = tf.keras.utils.to_categorical(y_train, num_classes=10)). But do just as follows

(x_train, y_train), (x_test, y_test) = tf.keras.datasets.cifar10.load_data()

# train set / data 
x_train = x_train.astype('float32') / 255

print(x_train.shape, y_train.shape) 
# (50000, 32, 32, 3) (50000, 1)

model ...
model.compile(
loss=tf.keras.losses.SparseCategoricalCrossentropy(from_logits=True),
....
)

And in predicting time don’t use np.argmax() on ground truth as they are already an integer now as we didn’t use tf.keras.utils.to_categorical this time.

print(np.argmax(y_pred, axis=1).shape, y_train.reshape(-1).shape)
# (50000,) (50000,)

y_pred = model.predict(x_train, verbose=2) # take prediction 
confusion = tf.math.confusion_matrix(
              labels = y_train.reshape(-1),             # get trule labels 
              predictions = np.argmax(y_pred, axis=1),  # get predicted labels
              )    

Now rest of the stuff is good to use.

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