How to write a confusion matrix in Python?

Question

I wrote a confusion matrix calculation code in Python:

def conf_mat(prob_arr, input_arr):
        # confusion matrix
        conf_arr = [[0, 0], [0, 0]]

            


        

Answer 1

You can make your code more concise and (sometimes) to run faster using numpy. For example, in two-classes case your function can be rewritten as (see mply.acc()):

def accuracy(actual, predicted):
    """accuracy = (tp + tn) / ts

    , where:    

        ts - Total Samples
        tp - True Positives
        tn - True Negatives
    """
    return (actual == predicted).sum() / float(len(actual))

, where:

actual    = (numpy.array(input_arr) == 2)
predicted = (numpy.array(prob_arr) < 0.5)