# How to find the indices of element occuring once in a vector?

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Hello all

I want to know...How can I get the indices of a value that is occuring only once in a vector...please guide.

Example: A=[1 1 0 -1 0 0 1 0 1 1]

Task: To identify the indices of -1 (as it is occuring only once) in A.

Please Help!!!

Regards

##### 0 Comments

### Accepted Answer

Cedric Wannaz
on 23 May 2014

Edited: Cedric Wannaz
on 23 May 2014

There are ways to solve your problem based on HISTC or ACCUMARRAY. However, the simplest approach if you really have only two situations (unique 1 or unique -1) is probably the following:

if sum( A == 1 ) == 1

pos = find( A == 1 ) ;

else

pos = find( A == -1 ) ;

end

value = A(pos) ;

##### 4 Comments

Cedric Wannaz
on 23 May 2014

Edited: Cedric Wannaz
on 23 May 2014

Well, I would personally go for clarity .. otherwise there is even a one liner actually:

[~,pos,value] = find( A .* (A == -1 + 2*(sum(A==1)==1)) )

### More Answers (3)

George Papazafeiropoulos
on 23 May 2014

Edited: George Papazafeiropoulos
on 23 May 2014

A=[1 1 0 -1 0 0 1 0 1 1];

[~,c]=histc(A,unique(A));

out=A(c==1);

##### 2 Comments

Cedric Wannaz
on 23 May 2014

Mahdi
on 23 May 2014

If you're looking specifically for the value of -1, you can use the following:

index1=find(A==-1)

George Papazafeiropoulos
on 23 May 2014

Edited: George Papazafeiropoulos
on 23 May 2014

A=[1 1 -1 0 0 0 1 0 1 1];

[~,c]=histc(A,unique(A));

out=find(c==1);

##### 3 Comments

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