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Use if / else inside a for-loop and change values of array depending on condition

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ARP
ARP on 9 Feb 2019
Commented: ARP on 9 Feb 2019
Hi all,
I am stuck with the following step and I can't find the solution. The code I need is to change the columns of an array depending on the column index. For odd numbers, without change, for even numbers change the sign.
The size of the array should be variable by dimensions 1 and 2.
Here is what I tryied. Can someone help me please.
Thanks
Size_1 = 5;
Size_2 = 6;
array = ones(Size_1,Size_2);
for i=1:Size_2
if rem(i,2)==0
new_array_2 = array(:,i);
else
new_array_2 = -1*array(:,i);
end
end
new_array should be this
new_array =
1 -1 1 -1 1 -1
1 -1 1 -1 1 -1
1 -1 1 -1 1 -1
1 -1 1 -1 1 -1
1 -1 1 -1 1 -1

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Accepted Answer

madhan ravi
madhan ravi on 9 Feb 2019
No loops needed:
size1=5;
size2=6;
A=ones(size1,size2);
A(:,2:2:end)=-A(:,2:2:end)

  2 Comments

ARP
ARP on 9 Feb 2019
Thanks!
I am still corious what I did wrong on my script. I will need to implement something like that later on. Specifically, to read if the folder number is even or uneven.
madhan ravi
madhan ravi on 9 Feb 2019
See the answer below.
Reasons:
  • You forgot to preallocate new_array_2.
  • You forgot to index new_array_2.

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More Answers (1)

madhan ravi
madhan ravi on 9 Feb 2019
If you insist loop then:
Size_1 = 5;
Size_2 = 6;
A = ones(Size_1,Size_2);
for i=1:Size_2
if rem(i,2)==0
A(:,i)=-A(:,i); % if even change the sign
else
A(:,i)=A(:,i);
end
end

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