how to find the index of first n occurrence of each unique value of a matrix

I have a 5915x1 matrix and there are 42 unique values in the matrix.I want to find out first 75 occurences of each unique value. suppose i have a column matrix A as

A={1 2 3 4 1 1 2 2 5 5 5 5 4 6 7 8 4 6 4 }

Then for 1 : [1,5,6]

      2:[2,7,8]
etc.

[Jan]

Just to clarify: The elements are not unique, otherwise you cannot find 75 occurrences.

Answer 1

[Azzi Abdelmalek]

A=randi(42,5915,1);
b=cell2mat(arrayfun(@(x) find(A==x,75),1:42,'un',0))'

[Tripti Malviya]

Thank you so much :)

[Tripti Malviya]

Hey will it not work for a double array.Coz its giving me an empty matrix as a result :(

Answer 2

[Andrei Bobrov]

A = randi(8,20,1); % eg
n = 4;

A1 = unique(A)
na = numel(A1);
out = [A1(:).';nan(n,na)];
for j1 = 1:na
    k = find(A == A1(j1),n);
    out(2:numel(k)+1,j1) = k;
end
out = out.';

[Tripti Malviya]

it doesnt give the desired output..