Find nearest value in numpy array


Question

Is there a numpy-thonic way, e.g. function, to find the nearest value in an array?

Example:

np.find_nearest( array, value )
1
285
5/7/2017 9:29:20 PM

Accepted Answer

import numpy as np
def find_nearest(array, value):
    array = np.asarray(array)
    idx = (np.abs(array - value)).argmin()
    return array[idx]

array = np.random.random(10)
print(array)
# [ 0.21069679  0.61290182  0.63425412  0.84635244  0.91599191  0.00213826
#   0.17104965  0.56874386  0.57319379  0.28719469]

value = 0.5

print(find_nearest(array, value))
# 0.568743859261
450
5/15/2018 10:57:25 AM

IF your array is sorted and is very large, this is a much faster solution:

def find_nearest(array,value):
    idx = np.searchsorted(array, value, side="left")
    if idx > 0 and (idx == len(array) or math.fabs(value - array[idx-1]) < math.fabs(value - array[idx])):
        return array[idx-1]
    else:
        return array[idx]

This scales to very large arrays. You can easily modify the above to sort in the method if you can't assume that the array is already sorted. It’s overkill for small arrays, but once they get large this is much faster.


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