Apply operations over each row in array (Python)

Question

I have an array (3 by 3) and need to output the same size array in which each value is divided by the cumulative sum over the row.

A = np.array([ [1,4,1], [4,1,9], [1,9,1]])
ideal_output = [[1/6, 4/6, 1/6], [4/14, 1/14, 9/14], [1/11, 9/11, 1/11]]

Current Code but this is outputting with wrong dimensions:

output = []
denom = 0
for i in A:
    value_sum = np.cumsum(i)
    denom += value_sum
for i in A:
    result= i / denom
    output.append(result)

Woodford · Accepted Answer · 2022-01-12 17:02:14Z

1

> A / A.sum(axis=0)[:,None]
array([[0.16666667, 0.66666667, 0.16666667],
       [0.28571429, 0.07142857, 0.64285714],
       [0.09090909, 0.81818182, 0.09090909]])

answered Jan 12, 2022 at 17:02

Woodford

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2 Comments

Michael Szczesny Over a year ago

This sums the columns (the example data is symetric: row and column sums are equal). A / A.sum(1, keepdims=True) avoids reshaping.

Woodford Over a year ago

@MichaelSzczesny Nice tip if your input is symmetric (I didn't notice that)! TIL about keepdims

Shunya · Accepted Answer · 2022-01-12 18:24:42Z

1

You can do this:

ideal_output = (A.T/A.sum(axis=1)).T

Hope this solved your problem

edited Jan 12, 2022 at 18:24

Shunya

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answered Jan 12, 2022 at 17:12

barnabas kouami

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