How to use variable names/strings in a For cycle
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Hugo
am 25 Jan. 2022
Beantwortet: Image Analyst
am 26 Jan. 2022
Hi,
I have the following code:
B1=matrix(:,1)
B2=matrix(:,2)
B3=matrix(:,3)
B4=matrix(:,4)
B5=matrix(:,5)
I would like to replace the 5 lines of code above by a "For" cycle.
However, I get an error when I try to compile the following code:
For i=1:5
"B"+i=i
end
The error is:
Incorrect use of '=' operator. Assign a value to a variable using '=' and compare values for equality using '=='.
How can I define variable names/strings correctly?
I thank you in advance,
Best regards,
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Stephen23
am 25 Jan. 2022
Bearbeitet: Stephen23
am 25 Jan. 2022
"How can I define variable names/strings correctly?"
Dynamically naming variables is one way that beginners force themselves into writing slow, complex, inefficient, obfuscated code that is buggy and difficult to debug. Here are some reasons why:
The simple and efficient MATLAB approach is to use indexing. Is there a particular reason why you cannot use indexing?
Here is simpler, much more efficient code that actually works (unlike your code):
for k = 1:5
vec = matrix(:,k);
end
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KSSV
am 25 Jan. 2022
You need not to do that.....it is sheer waste of time and not a good coding practise. You can save the data into a 3D matrix. This is preferred.
B = zeros(2,2,5) ;
B(:,:,1) = rand(2) ;
B(:,:,2) = rand(2) ;
B(:,:,3) = rand(2) ;
B(:,:,4) = rand(2) ;
B(:,:,5) = rand(2) ;
You can access them by using B(:,:,1),..B(:,:,5)
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Voss
am 25 Jan. 2022
Here is how you can do it:
matrix = magic(5);
for i = 1:5
eval(['B' num2str(i) '=matrix(:,' num2str(i) ');']);
end
whos()
Here is why you shouldn't do it: https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval
Here is what you should do instead:
clear variables
matrix = magic(5);
B = cell(1,size(matrix,2));
for i = 1:5
B{i} = matrix(:,i);
end
whos()
celldisp(B)
Or:
clear variables
matrix = magic(5);
B = num2cell(matrix,1);
whos()
celldisp(B)
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