How to find minimum value in each row while keeping array dimensions same using numpy?

Question

I've the following array:

np.array([[0.07704314, 0.46752589, 0.39533099, 0.35752864],
          [0.45813299, 0.02914078, 0.65307364, 0.58732429],
          [0.32757561, 0.32946822, 0.59821108, 0.45585825],
          [0.49054429, 0.68553148, 0.26657932, 0.38495586]])

I want to find the minimum value in each row of the array. How can I achieve this?

Expected answer:

[[0.07704314 0.         0.         0.        ]
 [0.         0.02914078 0.         0.        ]
 [0.32757561 0          0.         0.        ]
 [0.         0.         0.26657932 0.        ]]

Paul Panzer · Accepted Answer · 2019-03-14 16:15:39Z

1

You can use np.where like so:

np.where(a.argmin(1)[:,None]==np.arange(a.shape[1]), a, 0)

Or (more lines but potentially more efficient):

out = np.zeros_like(a)
idx = a.argmin(1)[:, None]
np.put_along_axis(out, idx, np.take_along_axis(a, idx, 1), 1)

edited Mar 14, 2019 at 16:15

answered Mar 14, 2019 at 16:09

Paul Panzer

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Comments

BENY · Accepted Answer · 2019-03-14 16:09:53Z

0

IIUC first find out out the min value of each line , then we base on the min value mask all min value in original array as True, using multiple(matrix) , get what we need as result

np.multiply(a,a==np.min(a,1)[:,None])
Out[225]: 
array([[0.07704314, 0.        , 0.        , 0.        ],
       [0.        , 0.02914078, 0.        , 0.        ],
       [0.32757561, 0.        , 0.        , 0.        ],
       [0.        , 0.        , 0.26657932, 0.        ]])

edited Mar 14, 2019 at 16:09

answered Mar 14, 2019 at 16:02

BENY

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1 Comment

Nils Werner Over a year ago

You can use the keepdims=True kwarg here.

Alexandru Martin · Accepted Answer · 2019-03-14 15:59:46Z

0

np.amin(a, axis=1) where a is your np array

answered Mar 14, 2019 at 15:59

Alexandru Martin

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2 Comments

Mj1992 Over a year ago

I want to maintain the dimensions and indices. I want to fill 0 where the values are not minimum. Your solution gives a single dimension array of min values.

Alexandru Martin Over a year ago

Yes, you are right. For some reason i didn't read the expected answer part. Sorry.

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