CODEWITHSUNDEEP
arraysmatlabvector
JohnnyF
JohnnyF

Reputation: 1101

Find unique elements of multiple arrays

Let say I have 3 MATs

X = [ 1 3 9 10 ];
Y = [ 1 9 11 20];
Z = [ 1 3 9 11 ];

Now I would like to find the values that appear only once, and to what array they belong to

Upvotes: 1

Views: 208

Answers (2)

EBH
EBH

Reputation: 10440

If you are only dealing with integers and your vectors are equally sized (all with the same number of elements), you can use histcounts for a quick search for unique elements:

X = [1 -3 9 10];
Y = [1 9 11 20];
Z = [1 3 9 11];
XYZ = [X(:) Y(:) Z(:)]; % one matrix with all vectors as columns
counts = histcounts(XYZ,min(XYZ(:)):max(XYZ(:))+1);
R = min(XYZ(:)):max(XYZ(:)); % range of the data
unkelem = R(counts==1);

and then locate them using a loop with find:

pos = zeros(size(unkelem));
counter = 1;
for k = unkelem
    [~,pos(counter)] = find(XYZ==k);
    counter = counter+1;
end
result = [unkelem;pos]

and you get:

result =

    -3     3    10    20
     1     3     1     2

so -3 3 10 20 are unique, and they appear at the 1 3 1 2 vectors, respectively.

Upvotes: 1

Erfan
Erfan

Reputation: 1927

I generalized EBH's answer to cover flexible number of arrays, arrays with different sizes and multidimensional arrays. This method also can only deal with integer-valued arrays:

function [uniq, id] = uniQ(varargin)
combo = [];
idx = [];
for ii = 1:nargin
    combo = [combo; varargin{ii}(:)]; % merge the arrays
    idx = [idx; ii*ones(numel(varargin{ii}), 1)];
end
counts = histcounts(combo, min(combo):max(combo)+1);
ids = find(counts == 1); % finding index of unique elements in combo
uniq = min(combo) - 1 + ids(:); % constructing array of unique elements in 'counts'
id = zeros(size(uniq));
for ii = 1:numel(uniq)
    ids = find(combo == uniq(ii), 1); % finding index of unique elements in 'combo'
    id(ii) = idx(ids); % assigning the corresponding index
end

And this is how it works:

[uniq, id] = uniQ([9, 4], 15, randi(12,3,3), magic(3))

uniq =

     1
     7
    11
    12
    15


id =

     4
     4
     3
     3
     2

Upvotes: 1

Related Questions