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mr mo
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Finding equal members in a vector

Asked by mr mo
on 17 Dec 2017
Latest activity Commented on by Star Strider
on 17 Dec 2017
Hi. My question is how can I find equal members in a vector with their indices.
For example I have this vector.
V = [ 10 13 10 20 10 95 70 13];
Thanks a lot.

  1 Comment

This has nothing to do with the MATLAB compiler product or the Coder product, or a GUI or 3-D plots, or nearly all the tags you applied. Save yourself some time and only put the relevant tags that will help people.

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4 Answers

Answer by jean claude on 17 Dec 2017

find(x==10)

  2 Comments

mr mo
on 17 Dec 2017
Assume that I don't know the values of the vector.
[a] = histc(x,unique(x));
t=unique(x);
c=find(a>1);
d=0;
for i=1:length(c);
d=[d find(x==t(c(i)))];
end
d(1)=[]; % d is the output

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Answer by YT
on 17 Dec 2017
Edited by YT
on 17 Dec 2017

Found your answer in this post

  2 Comments

mr mo
on 17 Dec 2017
In my question I want to have the below form of output
1 3 5
2 8
that indicates
V(1) = V(3) = V(5)
and
V(2) = V(8)
YT
on 17 Dec 2017
Something like this then?
clear C
V = [ 10 13 10 20 10 95 70 13];
unqV = unique(V);
for i = 1:length(unqV);
C{i,1} = unqV(i)
C{i,2} = find(V==unqV(i));
end
%C = {10,[1 3 5];
% 13,[2 8];
% 20,4;
% 70,7;
% 95,6}

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Answer by Star Strider
on 17 Dec 2017

If you only want the repeated values in the vector and their indices:
V = [ 10 13 10 20 10 95 70 13]; % Original Vector
[Vu,~,I] = unique(V(:), 'stable'); % Unique Values
Tally = accumarray(I, 1); % Count Occurrences
Idx = bsxfun(@eq, V, Vu(Tally > 1)) .* (1:length(V)); % Determine Indices Of Multiple Values Only
OutD = [Vu(Tally > 1) Idx] % Double Matrix Result
for k1 = 1:size(Idx,1)
IdxC{k1} = Idx(k1,(Idx(k1,:)>0)); % Keep Only Non-Zero Values
OutC{k1} = {OutD(k1,1) IdxC{k1}}; % Cell Array Result
end
celldisp(OutC) % View Cell Array (Optional)
OutD =
10 1 0 3 0 5 0 0 0
13 0 2 0 0 0 0 0 8
The ‘OutC’ cell array result eliminates the zeros in the ‘(2:end)’ columns of ‘OutD’.

  4 Comments

Show 1 older comment
You did not say the line that threw that error.
My code ran for me without error in R2017b, with the default ‘automatic expansion’.
Use these nested bsxfun calls instead:
Idx = bsxfun(@times, bsxfun(@eq, V, Vu(Tally > 1)), (1:length(V)));
mr mo
on 17 Dec 2017
Is there any possibility to use other command except bsxfun and accumarray ?
Not that I am aware of. It is necessary to accumarray (or one of the histogram functions) to count the occurrences. Using bsxfun is necessary to do the array calculations.

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Answer by Jos (10584)
on 17 Dec 2017

V = [ 10 13 10 20 10 95 70 13];
[VU, ~, j] = unique(V)
P = accumarray(j, 1:numel(V), [] ,@(x) {x})
% P{k} holds all the indices where V equals VU(k)

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