in matlab, find the array position of an entry closest to some arbitrary value

March 4th, 2006 by Lawrence David

a friend asked:

matlab question: i have an array of data. how do i get matlab to find the position of an entry closest to some arbitrary value?
for instance, i would have
a= [1; 4; 6; 8; 12]
i want to search for 9 and have matlab spit back 4, the entry in a closest to 9.

here’s one way to solve that problem (assuming that variable k=9):

>> [min_difference, array_position] = min(abs(a - k))

wheree array_position is the desired index value.

Posted in Matlab |

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25 Responses to “in matlab, find the array position of an entry closest to some arbitrary value”

on 01 Feb 2007 at 1:01 pm Cruchon

Something like
[rte,index]=min(abs(X-x0)); where x0 is the target and X is the array you want to search in works. The answer is index.
on 01 Feb 2007 at 1:08 pm Lawrence David

i believe that’s exactly what i wrote above.
on 29 May 2007 at 10:28 am Roman

Thanks guys!
on 20 Jul 2007 at 4:00 pm Hilikus

??? that returns the difference between the closest and the target vale not its INDEX
on 20 Jul 2007 at 4:13 pm lawrence

hilikus:

the second argument returned is the index; the first argument returned is the difference.
on 20 Jul 2007 at 4:21 pm Hilikus

Bah, nevermind, i didnt see the double output
on 15 Sep 2007 at 10:18 am D

>> [trash array_position] = min(abs(a - k))

probably should have a “,” or odd things may happen.

[trash, array_position] = min(abs(a - k))

I wasted a lot of time recently and that simple problem caused it.

D
on 29 Feb 2008 at 2:58 pm jess

I love you for this! *mwah*
on 05 Mar 2008 at 12:44 pm huzzzaa

thanks guys!!!!!!!!! saved me hours developing my own algorithm!
on 28 May 2008 at 12:43 pm Chan

Man, you guys really rock! Thanks a lot, saved me hours. Keep up the good work!!
on 27 Aug 2008 at 12:01 pm marchessoux

Thanks a lot, exacty what I needed, so economy of many time ;=)
Cédric
on 23 Sep 2008 at 11:44 am dave

can you do something similar but for several k’s at a time?
on 04 Dec 2008 at 2:23 am MoneyG

Is there a similar way to get position information out of a matrix.

I tried something like,
[row,col]=min(min(matrix))
but that returns only the final row that the element is in, not its exact location.
on 26 Dec 2008 at 5:50 pm Den Wald vor lauter Bäumen nicht sehen … « wAnNaBe NeRd

[...] to see the wood for the trees”. I guess it is also know to non-German speakers? I just found this very trivial, banal and easy Matlab command line, which makes my equivalent lines look very stupid and [...]
on 17 Feb 2009 at 4:02 am Tom

Nice! Saved me some time!
on 11 Mar 2009 at 5:29 am Sameer

How Matlab search the object or variable name in simulink model.
mean Functionality of Edit->Find…(Ctrl+F).
on 11 May 2009 at 12:03 pm cato

but what if you want to be sure you at the value closest to this value right/left side?

for instance, a cumulative probability vector and you want to find the index for the value that is the first above 0.5?
on 22 Aug 2009 at 2:59 pm efrain

greato!
thanks a lot!
on 27 Aug 2009 at 1:33 pm sharkey

Thanks for post this! You just made my life easier.
on 27 Aug 2009 at 1:35 pm sharkey

apparently, the space this took in my brain was previously occupied by my knowledge of the English language… sorry.

Thanks for posting this. You just made my life easier.
on 21 Nov 2009 at 6:53 pm penguin

you could use something like this for multiple ‘k’s (’range’ == ‘a’, ‘vector’ is a set of ‘k’s):

function inds = findClosest(range, vector)
% ‘flatten’ everything into row vectors
origshape = size(vector);
sz_r = size(range);
numTargets = sz_r(1) * sz_r(2);
numInputs = origshape(1) * origshape(2);

range = reshape(range, [1, numTargets]);
vector = reshape(vector, [1, numInputs]);

% find the difference between the target values and the actual values
% ‘range’ is replicated across columns,
% ‘vector’ is replicated across rows
diff = repmat(range’, 1, numInputs);
diff = diff - repmat(vector, numTargets, 1);
diff = abs(diff);

[vals, inds] = min(diff);
inds = reshape(inds, origshape);
end
on 09 Mar 2010 at 5:11 am Max

Much better than my routine, which always
gets confused by the extrema of the array.
And faster too, love it.
on 28 May 2010 at 6:53 am Multiple output arguments « Abandon MATLAB

[...] why multiple output arguments in Matlab were a poor design decision. But here is a start. In an unsuccessful attempt to find a code that’s less than O(N*M) in storage for a problem that in a…, I saw that someone on Yahoo! Answers wants to know, Is there a similar way to get position [...]
on 10 Aug 2010 at 3:04 pm Jay Mung

Hey Lawrence. Columbia BME ‘04 alum here. I googled for your little trick here and was pleasantly surprised to find your blog. Keep up the good work.

Jay
on 23 Aug 2010 at 11:54 am Alexander

Lawrence, I really enjoy your blog, I have found useful answers to many questions. This one was not the exception. Thanks a lot and keep up the great work.

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in matlab, find the array position of an entry closest to some arbitrary value

if that was helpful ...

25 Responses to “in matlab, find the array position of an entry closest to some arbitrary value”

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