How to find a unique (non-repeated) value in a matrix by using matlab

Question

everyone. Let's say I have following (3x3)matrix A:

0 1 3
0 0 3
0 0 0

My question is how to find out the unique value in that matrix by using matlab? In this case, the result should be 1. I have tried used the

value=unique(A)

but it returned a vector {0;1;3} is not what I want.

I much appreciate if you guys can help me solve this problem. Thank you!

Answer 1

Here is a short one

value = A(sum(bsxfun(@eq, A(:), A(:).'))==1);

It compares all pairs of elements in the matrix and counts how many times they are equal and returns the ones that have been counted only once.

Answer 2

Here is a one line alternative:

find(histc(A(:), 0:3)==1) - 1

or more generally:

find(histc(A(:), min(A(:)):max(A(:)))==1) + min(A(:)) - 1

OR to generalize it even further (to handle floats)

p = 0.1; %//Set a precision.
(find(histc(A(:), min(A(:)):p:max(A(:)))==1) + min(A(:)) - 1)*p

Answer 3

The method of counting I generally prefer uses sort and diff as follows,

[x,sortinds] = sort(A(:));
dx = diff(x);
thecount = diff(find([1; dx; 1]));
uniqueinds = [find(dx); numel(x)];
countwhat = x(uniqueinds);

Then you grab the value(s) with only one occurrence:

lonelyValues = countwhat(thecount==1)

If you want the location of these value(s) in the matrix:

valueInds = sortinds(uniqueinds(thecount==1))
[valRows,valCols] = ind2sub(size(A),valueInds)

If you expect to any NaN and/or Inf values in your matrix, you have to do additional bookkeeping, but the idea is the same.

Answer 4

Here is another alternative using unique() and hist():

count elements:

[elements,indices,~] = unique(A);              % get each value with index once
counts = hist(A(:), elements);                 % count occurrences of elements within a

get elements:

uniqueElements = elements(counts==1);          % find unique elements

get indices:

uniqueIndices  =  indices(counts==1);          % find unique indices
[uRow, uCol] = ind2sub(size(A),uniqueIndices); % get row/column representation