# How to get a for loop to update its iterations on a variable that can change.

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Eric Cheatwood on 11 Nov 2017
Answered: Image Analyst on 11 Nov 2017
Hi, I am working on a project that evaluates an EKG and this particular set of code I am having problems with checks if there is a t wave in between each set of QRS complexes. If no T is present, the QRS is consider a false positive and removed from the set. The problem I am having is if a QRS is removed, the for loop goes to the original length of the array. Is there a way to get the for loop to suspend its iterations early if the length of locqrs is shortened within the loop.
for n = 1:length(locqrs)-1
%Finding if there is a T between QRS n and QRS n+1.
tpres = find(loct > locqrs(n) & loct < locqrs(n+1));
%If else that removes QRS complex if tpres is zero.
if isempty(tpres) == 1
locqrs(n) = [];
ampqrs(n) = [];
widthqrs(n) = [];
promqrs(n) = [];
qrstelim = qrstelim +1;
else
end
%NN represents the R to R interval of the ECG signal.
NN(n) = locqrs(n+1) - locqrs(n);
n = n + 1;
end
KSSV on 11 Nov 2017
YOu can put a if condition with break if you want to come out of loop.

Image Analyst on 11 Nov 2017
You can't. If you change a loop iterator value within the for loop, it will change for the remainder of that iteration, but once it hits the "end" and begins the next iteration, it will take on the value it would have anyway, basically ignoring what you did.
What you need to do is to convert the for loop into a while loop. With a while loop, you can change variables inside.

Yogananda Jeppu on 11 Nov 2017
Looks like you have the data and you are doing post processing. Try not to use the for loop. Use the find for the complete array. You will get a set of indices. Remove them.