Find index of column in matrix using lambda (python)

Question

How can I find index of column with smallest sum of elements. I would like to find short solution which uses lambdas. For example for given matrix:

[[7, 2, 7, 2, 8],
 [2, 9, 4, 1, 7],
 [3, 8, 6, 2, 4],
 [2, 5, 2, 9, 1],
 [6, 6, 5, 4, 5]]

It should return 3. Because third column has smallest sum of elements.

akuiper · Accepted Answer · 2016-12-22 19:45:38Z

1

With numpy, you can sum by columns and use the argmin() to find out the minimum sum index:

import numpy as np
np.array(lst).sum(axis = 0).argmin()
# 3

Or you can use list comprehension without using numpy package:

min(((i, sum(v)) for i, v in enumerate(zip(*lst))), key = lambda x: x[1])[0]
# 3

answered Dec 22, 2016 at 19:41

akuiper

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2 Comments

Based on your sollution I've found even shorter sollution which uses straight Python: min(enumerate(map(sum,zip(*m))),key=lambda x:x[1])[0]

Not necessarily faster though since both approaches use only generators but surely a nicer and shorter one.