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# Need help with a while loop to take numbers off.

Asked by Nicolo Zaza on 21 Jul 2012

Alright so I have counting algorithm but i need it to extract elements from an original source and after extracting them and storing I need matlab to discard them so they dont get count again. How do i do this? My code: if true

```DATA = [ 60 0 40 -20 40 -40 50 -30 30 -60 0 -30 40 -30 60];
L = length(DATA);
E = [1:L];
N = 1;
while N < L
N = N + 1;
if N < 3
continue
end
X(N) = [abs(DATA(N)-DATA(N-1))];
Y(N) = [abs(DATA(N-1)-DATA(N-2))];
if X < Y
continue
else
RANGE(N) = Y(N);
XMEAN(N) = [.5*(DATA(N-1)+DATA(N-2))]
DATA (N -2) = []
DATA (N-1) = []
N = N - 2
end
for I = N:L
L = L - 2
E(I) = E(I+1);
end
end
end
```

## 1 Comment

Nicolo Zaza on 21 Jul 2012

Sorry to not finish expressing my question. So what I'm using right now is if true

```DATA(N-2) = []
&
DATA(N-1) = []
end
to delete the values used to calculate RANGE because once range is calculated I dont need to calculate it again for those same points. Is there a better matlab function/code to accomplish this need?
```

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Answer by Image Analyst on 21 Jul 2012
Edited by Image Analyst on 21 Jul 2012

Yes, that will delete elements but you're indexing elements and that will change, not to mention the length of your DATA array keeps getting shorter as you delete elements to eventually as N approaches L you'll get an index out of range error.

What are you really trying to do? Can't you just extract arrays and subtract them, and use diff? Or use hist if you want to count values?

```data_n = DATA(3:end)
data_nm1 = DATA(2:end-1)
data_nm2 = DATA(1:end-2)
X = abs(data_n - data_nm1)
Y = abs(data_n - data_nm2)
RANGE = y
xMean = 0.5 * (data_nm1 - data_nm2)
% I have no idea what E is supposed to represent.
```