Find a number and range of group of the same number

I have an array with numbers [1 1 1 1 1 1 1 2 2 2 2 3 3 3 3 1 1 2 2 1 1 3 3 3 3 3 1 1 1 2 2 2 ]

The array has the length: of 1x42502

I would like the number of how many repeats the same number, and the range of the specific repeat.

Output example:

number 1 has 4 repeats, range of the first repeat is: 1:6, range of the second repeat is: 15:16 , etc

number 2 has 3 repeats, range ...

number 3 has 2 repeats, range ...

How to do this?

Histcounts return sum of all repeat.

Answer 1

[Jan]

With FileExchange: RunLength :

a = [1 1 1 1 1 1 1 2 2 2 2 3 3 3 3 1 1 2 2 1 1 3 3 3 3 3 1 1 1 2 2 2];
[b, n, idx] = RunLength(a);
idxR   = [idx(:), idx(:) + n(:) - 1];

idxR = 9×2

1 7 8 11 12 15 16 17 18 19 20 21 22 26 27 29 30 32

ub     = unique(b);
result = splitapply(@(c) {c}, idxR, b(:));

result = 3×1 cell array
    {4×2 double}
    {3×2 double}
    {2×2 double}

result{ub(1)}  % Ranges, where e.g. ub(1), which equals 1, occurs:

ans = 4×2

1 7 16 17 20 21 27 29

If you do not have a C-compiler, use RunLength_M from the same submission.

Answer 2

[Bruno Luong]

A= [1 1 1 1 1 1 1 2 2 2 2 3 3 3 3 1 1 2 2 1 1 3 3 3 3 3 1 1 1 2 2 2 ];
[u,~,G]=unique(A);
n = length(u);
for g=1:n
    i = find(G==g);
    j = find([true; diff(i)>1; true]);
    start=i(j(1:end-1));
    stop=i(j(2:end)-1);
    m = length(start);
    fprintf('value=%g, %d intervals\n', u(g), m);
    fprintf('\t(%d:%d)\n', [start, stop]');
end

value=1, 4 intervals

	(1:7)
	(16:17)
	(20:21)
	(27:29)

value=2, 3 intervals

	(8:11)
	(18:19)
	(30:32)

value=3, 2 intervals

	(12:15)
	(22:26)

[Bruno Luong]

I think my approach is not good if the number of groups n is large. In this case one should use Jan's runlength.