How to extract data from an array

Hello. I have a signal with over 10mil data points. Whenever my signal crosses a certain threshhold i want to extract x numbers of point before and x numbers of point after it hit the threshhold.

IsEvent = true;

peakthreshhold = 120;

for i = 1:1:length(sig)

if (sig(i) >= peakthreshhold && IsEvent)

signal= (sig(i-20000):1:sig(i+50000));

disp(signal)

IsEvent = false;

end

end

so basically i wanted to extract 20000 points before it hit sig(i) to 50000 after it hit sig(i), so i get a new array with 70000 points extracted from sig(i).

If i run it now, i get 15 points

Answer 1

[Benjamin Thompson]

Use

signal= sig(i-20000:1:i+50000);

And you probably need checks in case i < 20000 or i > (end - 50000) as special cases.

Answer 2

[KSSV]

Let x be your signal and val be yout threshold.

val = 50000 ;
tol = 10^-3 ; 
idx = find(abs(sig-val)<=tol) ; % this gives the index of your threshold 
v1 = sig(1:idx) ;
v2 = sig(idx+1:end) ; 

[Peter Darrouj]

i changed

signal= (sig(i-20000):1:sig(i+50000));

to:

signal= sig((i-20000):(i+50000));

This seems to have fixed the problem.

I still need to test ur answer because it looks like an easier way, but i dont understand what you did.