# Index with for loop variable name and definition

조회 수: 183 (최근 30일)
Stef 2018년 6월 28일
편집: Stephen23 2018년 6월 29일
I have a matrix A and avector y. I want to create a loop which names and defines them the matrix A from A1,...,A10.
for i = 1:10
A{i} = X(y==i)
end
Unfortunately this code does not work. It would be nice to end up with a double and not a cell
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Stephen23 2018년 6월 29일
편집: Stephen23 2018년 6월 29일
"I want to create a loop which names and defines them the matrix A from A1,...,A10."
Dynamically accessing variable names is one way that beginners force themselves into writing slow, complex buggy, code. Read this to know why:
Using a cell array with indexing is simple, neat, and very efficient. You should use a cell array with indexing.
Note that when you put a number into the variable name like that then you are using it as pseudo-indexing: note that processing pseudo-indexing is complex and slow. In contrast, real indexing of a cell array (as your question shows) is extremely fast, efficient, and easy to debug.
So far you have not provided any reason why you need to write much slower, more complex, buggier code. Cell arrays are designed to efficiently hold data arrays, exactly like you want to now.

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### 채택된 답변

D. Plotnick 2018년 6월 29일
If I understand your question, it is parallel to the one here, which as Stephen Cobeldick points out is a bad idea.
There is sort of a way around this using a structure.
for i = 1:10
fname = ['A',num2str(i)];
B.(fname) = y(i);
end
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Stef 2018년 6월 29일
Thanks, it worked!
Stephen23 2018년 6월 29일
편집: Stephen23 2018년 6월 29일
@Stef: note that your original code, using a cell array and indexing, is faster and simpler than this answer.
You might also find this to be of interest:

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