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Unable to remove elements from array and I don't know why

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Garrett Higgins
Garrett Higgins on 12 Jan 2021
Commented: Stephen Cobeldick on 12 Jan 2021
I have been using matlab for a few years but I just am having one of those days and cannot figure out what is going on here. I have two arbitrary arrays, I iterate and take the distance of each point. If that distance is below 10, I want to remove those elements from the array, therefore shortening the array. The error I'm getting is in the asteriks.
************************************
A null assignment can have only one non-colon index.
Error in LoopTesting (line 10)
x(1,i)=[];
***********************************
Please explain to me why this is happening. Thank you!
y = [1 2 3 4 5 6 7 7 8 8 9 9 10 10];
x = [4 5 6 1 2 3 4 5 6 7 8 8 9 10];
xc = 15;
yc = 15;
for i=1:length(x)
d=sqrt(((xc-x(i))^2)+(yc-y(i))^2);
if d < 10
x(1,i)=[];
y(1,i)=[];
end
end
length(x)
length(y)
  1 Comment
Stephen Cobeldick
Stephen Cobeldick on 12 Jan 2021
The problem is that once you remove an element the vector is shorter, but your loop still attempts to index into elements that no longer exist (because you have just shortened the vector). To avoid this either:
  • loop over the vectors backwards
  • collect an index (e.g. a logical vector) and remove the elements at once after the loop

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Answers (1)

Fangjun Jiang
Fangjun Jiang on 12 Jan 2021
Edited: Fangjun Jiang on 12 Jan 2021
Do the loop backward should resolve the problem. I hope you would understand the reason.
for i=length(x):-1:1
Also, better to use x(i)=[] since it is a vector.

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