Given a vector, how to pair them by nearest?

Hi,

I have a vector with values. I have to pair them by nearest.

Is there any magic command to do it?

Thanks!

Answer 1

[Sean de Wolski]

doc knnsearch

If you have the Statistics Toolbox this sounds like your magic command.

Of course, if you just need a magic command, you can always run:

magic(5)

More Using knnsearch here is probably overkill when you could just use a for-loop, finding the minimum of the exclusive set. But here is how I would do this with knnsearch:

[idx,D] = knnsearch(values',values','K',2)  %Get two because the first will be the value itself

idx(:,2)  %2nd column is the closest one that isn't the same
D(:,2)    %Distance
values(idx(:,2))  %What was the original value?

[Sean de Wolski]

You could also use pdist which might be faster.

[Dani Tormo]

I found knnsearch before but I cannot figure out how to use it for my purpose, X and Y have to be arrays.

My vector could be this one:

 values = [1.5 0.6 1.9 0.4 1.3 0.1];

How to pair them using knnsearch or pdist?

[Sean de Wolski]

So you have values, and you want to know the closest element from each in it? So 0.1 would pair with 0.4 which would pair with 0.6?

[Sean de Wolski]

See More

[Dani Tormo]

No because when two are paired it excludes from pairing with others. And the sum of all differences will have to be the minimum.

For example, if we pair this way:

• 0.6 and 0.4
• 1.5 and 1.3
• 1.9 and 0.1

and summing the total differences, it gives us 2.2.

But if we pair them like this:

• 0.1 and 0.4
• 1.9 and 1.5
• 0.6 and 1.3

it gives a total difference of 1.4. This result will be better than the previous one.

[Teja Muppirala]

Assuming an even number of elements, isn't the answer just SORTing the vector and taking two at a time?

values = [1.5 0.6 1.9 0.4 1.3 0.1];
reshape(sort(values),2,[])'

[Dani Tormo]

Yes man, you're right.

I wrote a program to evaluate random values, I run it for several minutes and sorting them and grouping always gives the minimum value.

Thanks for your help and time!

Answer 2

[Jos (10584)]

What do you mean by ' pair them by nearest '? Do you want to SORT the values?

Otherwise, can you give a small example of your vector and the required result of such a magic function?

[Dani Tormo]

I answered your question on the Sean's answer.