Finding equal members in a vector

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.

[Image Analyst]

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Answer 1

[jean claude]

   find(x==10)

[mr mo]

Assume that I don't know the values of the vector.

[jean claude]

 [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

Answer 2

[YT]

Found your answer in this post

[mr mo]

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]

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}

Answer 3

[Star Strider]

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’.

[mr mo]

for the first code I have this error

 Error using  .* 
 Matrix dimensions must agree.

[Star Strider]

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]

Is there any possibility to use other command except bsxfun and accumarray ?

[Star Strider]

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.

Answer 4

[Jos (10584)]

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)