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

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

Answer 1

[Cedric]

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) ;

[Sameer]

Hi...Thanks a lot for replying....its able to find the correct value. And to solve my purpose I just have to add a line which was suggested by mahdi. Thanks a lot...:)

Regards

[Cedric]

Note that you can contract this into a 2 liners

 pos   = find( A == (-1 + 2 * (sum(A==1) == 1)) ) ;
 value = A(pos) ;

but you lose in clarity.

[Mahdi]

Very nice Cedric! I didn't even think of doing that way!

[Cedric]

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)) )

Answer 2

[George Papazafeiropoulos]

A=[1 1 0 -1 0 0 1 0 1 1];
[~,c]=histc(A,unique(A));
out=A(c==1);

[Sameer]

Hi...Thanks for replying.

I want to know the index of an entry which is unique to a particulat set of values. lets say

if A=[1 1 1 -1 0 0] then I want the indices of -1. if A=[-1 -1 -1 0 1 0] then I want the indices of 1.

I hope I made it clear what I am looking for.

Awaiting your Reply.

Regards

[Cedric]

Sagar, you should take the time to understand his example. In particular, see what c is, what c==1 is, etc. Maybe read about logical indexing, and if you cannot use the latter and really need the position of unique element(s), read about FIND.

Answer 3

[Mahdi]

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

index1=find(A==-1)

[Sameer]

Hi...Thanks for replying.

I want to know the index of an entry which is unique to a particulat set of values. lets say

if A=[1 1 1 -1 0 0] then I want the indices of -1. if A=[-1 -1 -1 0 1 0] then I want the indices of 1.

I hope I made it clear what I am looking for.

Awaiting your Reply.

Regards

[Mahdi]

You can use the unique function.

[C, ia, ic]=unique(A)

Where the matrix C gives the unique value (1 or -1 in this case), and ia gives the indices where these are found.

[Sameer]

Thank you....but unique command returns the values that are present in the vector so here it is -1 0 1. But I am looking for the single value that is either 1 or -1 and then the indices of that particular value.

Regards

Answer 4

[George Papazafeiropoulos]

A=[1 1 -1 0 0 0 1 0 1 1];
[~,c]=histc(A,unique(A));
out=find(c==1);

[Sameer]

Thank you...I appreciate your help. But the above solution is confined to a particular A(i guess) and its returing the indicies of only -1 if the elements of A changes.

Actually I have large number of different vectors and in each either 1 or -1 is unique (either only 1 or -1 in a vector like A=[1,1,1,-1,0,0] (-1 is occuring once),B=[-1,-1,-1,1,0,0](1 is occuring once)) so for A i should have the indices of -1 for B indices of 1. so I am looking for a code which will determine the unique number in a vector and return its corresponding indices and only of that particular number...not like unique function.

Awaiting your reply.

Regards

[George Papazafeiropoulos]

Try the above code for different A. Define A as you want and then execute the two last lines of the code. I think it works...

[Sameer]

Unfortunately its not working as in the attached image you can see that 1 is the unique and its index should be 7 but the code is showing for -1 instead that is 1 2 3. where A=[-1 -1 -1 0 0 0 1 0].

Awaiting your response.

Regards