Minimum x and y coordinate of 2d array. Python

Question

I have a nx2 array where the first column represents x-coordinates and the second column y-coordinates, for example:

array = np.array([0,3],
                 [1,5],
                 [2,1],
                 [3,2])

How can I obtain the minimum y-coordinate with the corresponding x-coordinate returned allong with it? In the example, I want [1,2] returned, where 2 is the row index, not the numerical value contained in the array, but 1 is the actual numerical value.

I know I can simply use np.amin(array[:,1]) to obtain the minimum y-coordinate, but this doesn't give me any info of what x-coordinate corresponds to the y-minimum.

I have looked at the documentation of np.amin to see if it can return two parameters but it does not look like it can.

Back2Basics · Accepted Answer · 2015-03-20 06:49:00Z

1

array[np.argmin(array[:,1])][0]

You want to reference array values like this in a 2d array.

array[column][row]

np.argmin will give you the smallest number's index in the column and array*[0] will give the first element in the row

edited Mar 20, 2015 at 6:49

answered Mar 20, 2015 at 6:35

Back2Basics

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1 Comment

Jonny Over a year ago

Thanks, argmin is indeed the function I was looking for!

Ashwini Chaudhary · Accepted Answer · 2015-03-20 06:32:54Z

1

Perhaps something like this:

>>> index = array[:, 1].argmin()
>>> np.unravel_index((index * 2) + 1, array.shape)
(2, 1)
# reverse to get the column index first.
>>> np.unravel_index((index * 2) + 1, array.shape)[::-1]
(1, 2)

answered Mar 20, 2015 at 6:32

Ashwini Chaudhary

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