Select sequence of numbers from Array

Lets say I have an array like so:

[1 1 1 2 2 2 3 3 3 4 4 4 1 1 1 2 2 2 3 3 3 4 4 4 1 1 1 2 2 2 3 3 3 4 4 4 1 1 1 2 2 2 3 3 3 4 4 4]

(my real array is 3635 long)

I want to make a new array which shows which indexes have an nth time of sequence of 1's.

So like this:

the 3rd time the 1's are in sequence so in this case i would like it to return: [37 38 39]

[Dyuman Joshi]

Is the real array same/similar as this one? Because there's a repeating pattern here so you can easily get the indices.

Answer 1

[Stephen23]

V = [1 1 1 2 2 2 3 3 3 4 4 4 1 1 1 2 2 2 3 3 3 4 4 4 1 1 1 2 2 2 3 3 3 4 4 4 1 1 1 2 2 2 3 3 3 4 4 4];
X = V(:)==1;
Y = cumsum(diff([0;X])>0);
Z = 1:numel(V);
C = accumarray(Y(X),Z(X),[],@(a){a})

C = 4×1 cell array
    {3×1 double}
    {3×1 double}
    {3×1 double}
    {3×1 double}

C{:}

ans = 3×1

1 2 3

ans = 3×1

13 14 15

ans = 3×1

25 26 27

ans = 3×1

37 38 39