Get index of the element nearest to the given value

Question

The given value is 6.6. But the value 6.6 is not in the array (data below). But the nearest value to the given value is 6.7. How can I get this position?

import numpy as np
data = np.array([[2.0, 3.0, 6.5, 6.5, 12.0],[1,2,3,4,5]],dtype=float)

This is also similar: http://stackoverflow.com/questions/8527952/nearest-neighbor-search-in-python-without-k-d-tree — merlin2011, Apr 26 '14 at 08:11
@YuvalAdam looking for more direct way of doing it.@merlin2011 — , Apr 26 '14 at 08:30
Can you assume the array is sorted? Please provide more detail. — EML, Apr 26 '14 at 08:32
@EML The index position should be exact to the original array — , Apr 26 '14 at 08:34
What do you mean by a more "direct" way? Looking at offsets seems to be the best way to do it. — vinit_ivar, Apr 26 '14 at 08:39
i am meaning functions available in numpy or scipy@vinit_ivar — , Apr 26 '14 at 08:45

venpa · Answer 1 · 2014-04-26T09:11:58.523

3

You can get like this:

data[(np.fabs(data-6.6)).argmin(axis=0)]

output:

6.7

find the absolute diff on each element
Find the minimum from the result and get the element from index

EDIT: for 2d:

If it is python 2.x:

map(lambda x:x[(np.fabs(x-6.6)).argmin(axis=0)], data)

python 3.x:

[r for r in map(lambda x:x[(np.fabs(x-6.6)).argmin(axis=0)], data)]

results in returning nearest value in each row.

One value from all:

data=data.flatten()
print data[(np.fabs(data-6.6)).argmin(axis=0)]

index position from each row:

ip = map(lambda x:(np.fabs(x-6.6)).argmin(axis=0), data)

edited Apr 26 '14 at 09:11

answered Apr 26 '14 at 08:39

venpa

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The data shape is 2d array – Apr 26 '14 at 08:49
In your original question it was not 2d. Can you tell me you want one nearest value from all or you want minimum value for each row? – venpa Apr 26 '14 at 08:52
one nearest value from all – Apr 26 '14 at 08:53
sorry that i changed into 2d because i did mistake while posting – Apr 26 '14 at 08:54
Please find my edited answer. – venpa Apr 26 '14 at 08:58
i do not need for each row. one nearest value from the whole array is ok. – Apr 26 '14 at 09:01
ok..i have edited for the same... – venpa Apr 26 '14 at 09:07
no no i first need the index position in 2d array, then i can get the value – Apr 26 '14 at 09:08
one nearest index position over whole array – Apr 26 '14 at 09:09
Please find last line of the answer... – venpa Apr 26 '14 at 09:12
the result should be in the form that np.where function gives the index of.. – Apr 26 '14 at 09:14
your code given [2,4] as the answer is not associated with the expected answer – Apr 26 '14 at 09:16
yes...thats the index value of each rows. can you show me your syntax for np.where? – venpa Apr 26 '14 at 09:23

score 1 · Accepted Answer · answered Apr 26 '14 at 11:21

1

This is the simplest way I think.

>>> data = np.array([[2.0, 3.0, 6.5, 6.5, 12.0],[1,2,3,4,5]], dtype=float)
>>> data2 = np.fabs(data - 6.6)
>>> np.unravel_index(data2.argmin(), data2.shape)
(0, 2)

See np.argmin and np.unravel_index function.

answered Apr 26 '14 at 11:21

Kei Minagawa

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Get index of the element nearest to the given value

2 Answers2