Sum two columns of a numpy array and add it as a third column of the array

Question

I have following numpy array

X = np.random.random_integers(100000000,size=(100000000,2))

now I want to dd both the columns of the array to generate the third column of the array. I am trying X[3] = X[0]+X[1] but its shape is (2,).

Example final array :

10    5    15
15    6    21

yatu · Accepted Answer · 2019-07-09 09:37:56Z

5

You could np.concatenate with the sum along the last axis. An additional axis must be added to the result of X.sum(1), as all arrays to be concatenated must have the same number of dimensions. This can be done either with None/np.newaxis:

np.concatenate([X, X.sum(1)[:,None]], -1)

edited Jul 9, 2019 at 9:37

answered Jul 9, 2019 at 9:35

yatu

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3 Comments

Salman Arshad Over a year ago

what is the purpose of [:,None]

yatu Over a year ago

It adds an axis to X.sum(1), as all arrays to concatenate must have the same number of dimensions @salman

user3483203 Over a year ago

@SalmanArshad you can also use keepdims=True in sum, which removes the need for the extra broadcast

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