Select sequence of numbers from Array

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Jochem
Jochem on 2 Feb 2023
Commented: Dyuman Joshi on 2 Feb 2023
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]
  1 Comment
Dyuman Joshi
Dyuman Joshi on 2 Feb 2023
Is the real array same/similar as this one? Because there's a repeating pattern here so you can easily get the indices.

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Answers (1)

Stephen23
Stephen23 on 2 Feb 2023
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

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