Problem array initialization when storing Data

I red in some Data and stored it in a vector(A). Now I want to delet the first 200 entrys. I'm using a for loop for that. Strangely, I get the error: Matrix index is out of range for deletion. So when I look for the lenght of my 2 vectors, one is just half the length of the other:

   fname = tabularTextDatastore('curves.dat');
L = read(fname);%3 values all separated by a space bar
x = L(:,3);%vector with values of column3
y = L(:,2);%vector with values of column2
z = L(:,1);vector with values of column1
q = linspace(0,99,100);
A = table2array(x)
W = A;

 for i=1:200
    W(i) = [];
end
W
q1 = q(:);
%plot(q1,A)

Can somebody pleas explain me, why W has not the same length as A?

[Mischa Kim]

Please attach the entire code so we can help diagnose.

Answer 1

[Guillaume]

I want to delet the first 200 entrys. I'm using a for loop for that.

Always a bad idea. Most beginners never implement that properly

for i=1:200
   W(i) = [];
end

So, at i = 1, you delete the first element. So far so good. After that deletion, what was element 2 is now element 1, what was element 3 is now 2, etc.

Next step, i = 2. You delete the element at that index, but that element is what was element 3. So far, you've deleted element 1 and 3. What was element 2 is still 1, what was element 4 is now 2, what was element 5 is now 3, etc.

Next step, i = 3. You delete the element at that index. That was element 5. You get the picture. It's not working at all.

Don't use loops for deletion, particularly as there's a much simpler way:

W(1:200) = [];  %delete first 200 elements in one go

[Lukas Goldschmied]

Thanks for your help! That makes total sense. So with your way of deletion, I can also delet the last 200 elemets by typing:

   W(100:300) = [];

and delet the first 100 and the last 100 by typing:

 W(1:100)=[];
 W(100:200) = [];

[Guillaume]

Note that 100:300 is 201 elements, not 200.

W(101:300) = [];

will indeed delete the last 200 elements of W if and only if W has 300 elements. To be guaranteed to delete the last 200 elements regardless of the number of elements in W:

W(end-199:end) = [];

To delete the first 100 and last 100 regardless of the number of elements:

W([1:100, end-99:end]) = [];