How to reference a cell in a matrix only if it is preceded by a specific number?

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SRB 2018-8-20

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回答： dpb 2018-8-20

I have a 588x2 matrix. The first column are times associated with an event and the second column is a number representing the type of event that occurred. I would like to put certain events and the times they occurred into a different matrix. Specifically, I want events labeled "4" but only if they are preceded by events labeled "16". Any help is appreciated.

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Answer 1

OCDER 2018-8-20

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A = [rand(10, 1) [16 4 15 6 16 4 4 16 4 3]'];
Idx = find(A(1:end-1, 2) == 16 & A(2:end, 2) == 4) + 1;
B = A(Idx, :)
A =
3299   16.0000
9418    4.0000
0822   15.0000
5926    6.0000
2277   16.0000
9691    4.0000
5915    4.0000
5162   16.0000
9827    4.0000
2968    3.0000
B =
9418    4.0000
9691    4.0000
9827    4.0000

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Answer 2

dpb 2018-8-20

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This can probably somehow be done w/ the events objects in the timeseries; the overview doc talks about finding patterns but I've yet to figure out just how it is really helpful for such and can't find any examples in the doc to match the description...

So, way I'd do this would be something like

ev=[e [0;diff(e)]];                            % build event lookup table
event=[16 4];                                  % the event vector to match
ix=find(ismember(ev,[event(2) diff(event)]]);  % index to matching event in original array

using e for the 2nd column of data in the matrix.