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pythonconfusion-matrix

Dividing arrays in Python for confusion matrix

I have an object, 2x2, and I want to divide it by a 2x1, such that the first component divides the first row, and the second divides the second row. How can I do that?

cm = sklearn.metrics.confusion_matrix(Y1,Y2)
cm_sum = np.sum(cm, axis=1)
cm_perc = cm /  cm_sum.astype(float) * 100
Solution

  • You just need to have the right dimension. The one you are dividing has to be a column vector. We use .rehshape(-1,1) to accomplish that.

    a = np.array([[2,3], [5,6]])
print(a)
b = np.array([2, 4]).reshape(-1, 1)
print(b)
print(a/b)

    Output

    [[2 3]
 [5 6]]
[[2]
 [4]]
[[1.   1.5 ]
 [1.25 1.5 ]]

    So your code then will be -

    Y1 = [1,0,1,0]
Y2 = [0,0,1,0]
cm = metrics.confusion_matrix(Y1,Y2)
cm_sum = np.sum(cm, axis=1).reshape(-1,1)
cm_perc = cm / cm_sum

    You could also use the keepdims argument in np.sum that will basically keep the dimensions and the output will be a column vector in this case. So -

    cm_sum = np.sum(cm, axis=1, keepdims=True)

    will also work.