Getting the minimum indexes with numpy Python

Question

I am trying to get the index values of the function. But I want to get the minimum instead of the maximum values of just like the post: post. I have tried to convert the function below to work for the minimum values unlike the maximum values to getting the indexes.

Max Values:

a = numpy.array([11, 2, 33, 4, 5, 68, 7])
b = numpy.array([0, 4])
min = numpy.minimum.reduceat(a,b)

Index Function

def numpy_argmin_reduceat_v2(a, b):
    n = a.min()+1  # limit-offset
    id_arr = np.zeros(a.size,dtype=int)
    id_arr[b[1:]] = 1
    shift = n*id_arr.cumsum()
    sortidx = (a+shift).argsort()
    grp_shifted_argmin = np.append(b[1:],a.size)-1
    return sortidx[grp_shifted_argmin] - b

Have you tried numpy.argmin: numpy.org/doc/stable/reference/generated/numpy.argmin.html — ai2ys
– ai2ys, Commented Jan 30, 2021 at 13:36

jakevdp · Accepted Answer · 2021-01-30 21:02:49Z

1

For the minimum, you need the first item in each group rather than the last. This is accomplished by modifying grp_shifted_argmin:

def numpy_argmin_reduceat_v2(a, b):
    n = a.max() + 1  # limit-offset
    id_arr = np.zeros(a.size,dtype=int)
    id_arr[b[1:]] = 1
    shift = n*id_arr.cumsum()
    sortidx = (a+shift).argsort()
    grp_shifted_argmin = b
    return sortidx[grp_shifted_argmin] - b

This correctly returns the index of the minimum value within each sublist:

a = numpy.array([11, 2, 33, 4, 5, 68, 7])
b = numpy.array([0, 4])
print(numpy_argmin_reduceat_v2(a, b))
# [1 0]

print([np.argmin(a[b[0]:b[1]]), np.argmin(a[b[1]:])])
# [1, 0]

edited Jan 30, 2021 at 21:02

answered Jan 30, 2021 at 14:32

jakevdp

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3 Comments

tony selcuk Over a year ago

Sorry I updated the details what if the list was random,. I want to get the minimum between the 2 indexes.

jakevdp Over a year ago

That's exactly what this function does; see the example I added to the answer.

tony selcuk Over a year ago

Hey you have answered my questions a few months ago could you take a look at this post: stackoverflow.com/questions/67680199/…. it is related to this question.

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