Finding maxima in blocks of data, consecutively
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Problem Statement: I have a time series, x. I am interested in consecutive, temporal blocks of x where x > value. I also want to focus on blocks that are at least time "T" apart. Let x(*) indicate x at time index *. If:
x(m-K), x(m-K+1), x(m-K+2), ...x(m) > value
and, later at n > m + T (a greater time)
x(n-K), x(n-K+1), x(n-K+2), ...x(n) > value
I want to identify the maximal value within each block, while ignoring all temporally consecutive blocks that are less than T samples apart. I currently have a for loops-method that works, but it's clumsy and not great for the application I have in mind.
Application: I am trying to detect certain events, where x exceeds a detection statistic, but I only want events spaced "T" distance apart. Events closer than "T" are considered to be the same.
HELP? Thanks.
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Accepted Answer
Image Analyst
on 16 May 2013
Can't you just say
maxValue = max(x(n-K:n));
or similar for m? If you have the Image Processing Toolbox, you can use imdilate(), which is a sliding local maximum. If you want to get the max only of x with values greater than value, then
thresholdedX = x(x>value);
but then I'm not sure if the (n-K) and n apply to the indexes before or after thresholding and extraction of the values above the threshold value, so I can't give the next step for certain.
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Image Analyst
on 16 May 2013
Do you have the Image Processing Toolbox? If so you can do this easily. Just threshold and mask and pass to imdilate, then mask again. It's like 4 lines of code.
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