Visualizing a confusion matrix

A confusion matrix is a table that we use to understand the performance of a classification model. This helps us understand how we classify testing data into different classes. When we want to fine-tune our algorithms, we need to understand how data gets misclassified before we make these changes. Some classes are worse than others, and the confusion matrix will help us understand this. Let's look at the following:

In the preceding diagram, we can see how we categorize data into different classes. Ideally, we want all the non-diagonal elements to be 0. This would indicate perfect classification! Let's consider class 0. Overall, 52 items actually belong to class 0. We get 52 if we sum up the numbers in the first row. Now, 45 of these items are being predicted correctly, but our classifier says that 4 of them belong to class 1 and three of them belong to class 2. We can apply the same analysis to the remaining 2 rows as well. An interesting thing to note is that 11 items from class 1 are misclassified as class 0. This constitutes around 16% of the datapoints in this class. This is an insight that we can use to optimize our model.