How do I dynamically assign subsets of array data to unique variables without a loop?

Question

Brad 2016-11-2

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/310340-how-do-i-dynamically-assign-subsets-of-array-data-to-unique-variables-without-a-loop

编辑： Stephen23 2016-11-2

I’ve got a 4x5 double array of data that looks like this;

1  11  111  1111
2  22  222  2222
3  33  333  3333
4  44  444  4444

I’m attempting to dynamically assign rows of double array data to variables based on the unique values in column 1, using the following code;

clear all;
clc;
% Some random sample data
data = [11 1 11 111 1111; 22 2 22 222 2222; 11 3 33 333 3333; 22 4 44 444 4444];
% Find the unique values in column 1
Unique_Data_Rows = unique(data(:,1));
% Assign rows of data to Subset, then to a unique variable name as doubles.
for i = 1:length(Unique_Data_Rows)
      Index{i} = find(data(:,1) == Unique_Data_Rows(i)); %#ok<*SAGROW>
      Subset{i} = data(Index{i}, :);
end

Finding the data is not a problem. But assigning the data to individual variables has me wondering if I have a less than ideal approach. In reading the FAQs and several comments, it also seems this is a really bad practice that could lead to a lot of unintended consequences.

For this particular problem, what would be the smart approach when the desired output is comprised of a pair of 2 x 5 double arrays?

Subset1 =
          11           1          11         111        1111
          11           3          33         333        3333
Subset2 =
          22           2          22         222        2222
          22           4          44         444        4444

Any ideas are appreciated. Thank you.

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Adam 2016-11-2

Well, the question extends to why that is the desired output really. If that absolutely has to be it then you will have to do some ugly coding, but where are these used next that requires them to be in separate variables rather than still all in one?

Stephen23 2016-11-2

编辑：Stephen23 2016-11-2

@Brad: assigning to separate individual variables will be slow and buggy. You will not find any advanced users doing this in their own code, and you will not find any advanced users recommending doing this. Read this to know why:

https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval

In almost all cases when beginners wish to assign dynamically to variables the much better solution is to simply learn how to use indexing (perhaps in conjunctions with cell arrays or N-D arrays).

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