index of an array multiple same element

How can find the index of an array element if it have element have the same value for example a=[7 8 8 2 5 6 6 2 6 8] what is the index of third 8 and 6. I used find(A==8,1, firs) this gave the first one only, and how can I know the element have more than one value.

[madhan ravi]

what’s your expected output?

[Arkanra Kadhum]

the index of 7 is 1

first 8 is 2, second 8 is 3, third 8 is 10

first 6 is 6, second 6 is 7, third 8 is 9

i

Answer 1

[Stephen23]

>> a = [7,8,8,2,5,6,6,2,6,8];
>> U = unique(a) % the order is the same as C.
U =
   2   5   6   7   8
>> [R,C] = find(U(:)==a);
>> C = accumarray(R,C,[],@(v){v});
>> C{:} % same order as U.
ans =
    4
    8
ans =
    5
ans =
    6
    7
    9
ans =
    1
ans =
    2
    3
   10

Answer 2

[Andrei Bobrov]

[a1,~,ii] = unique(a,'stable');
out = [num2cell(a1(:)),accumarray(ii,(1:numel(ii))',[],@(x){sort(x)})];

[Arkanra Kadhum]

Hi Andrei

I try this code

a1=7; a2=8; a3=8; a4=2; a5=5 ;a6=6; a7=6; a8=2;a9=6; a10=8;

A=[ a1, a2, a3, a5, a4, a6,a7,a8,a9,a10];

[a1,~,ii] = unique(A,'stable');

out = [num2cell,a1(:)accumarray(ii,(1:numel(ii))',[],@(x){x})];

[a2,~,ii] = unique(A,'stable');

out = [num2cell,a2(:)accumarray(ii,(1:numel(ii))',[],@(x){x})];

I gate this error

out = [num2cell,a1(:)accumarray(ii,(1:numel(ii))',[],@(x){x})];

↑

Error: Unexpected MATLAB expression.

[Andrei Bobrov]

I'm fixed my typo in answer:

[a1,~,ii] = unique(a,'stable');
out = [num2cell(a1(:)),accumarray(ii,(1:numel(ii))',[],@(x){sort(x)})];

Answer 3

[madhan ravi]

u=unique(a);
C=arrayfun(@(x) find(a==u(x)),1:numel(u),'un',0);
%celldisp(C)

[madhan ravi]

If you want the order to be preserved then use 'stable' as an option in unique.