is there a way to perform this task w/o using loops?

Question

Jeffrey 2023-11-29

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2053437-is-there-a-way-to-perform-this-task-w-o-using-loops

评论： Jeffrey 2023-12-2

% this script sets up a structure p.  In this minimal version, p only contains 1 variable.
% then expands it into a 1x4 structure array q 
% and inserts values into one of the variables.  (Only the L variable is shown here.)
% and then retrieves the values
% The variable is a row vector and has name given by varName
% The values go into (and are retrieved from) the 2nd element of L because varIndex = 2;
p.varName = 'L';
p.varIndex = 2;
p.L = [3, 4, 5];
nval = 4;
q = repmat(p,1,nval);
vals = [6 7 8 9];
% Insert values
for i=1:nval
    q(i).(p.varName)(p.varIndex) = vals(i);
end
Xv = zeros(1,nval);
% Retrieve values
for i=1:nval
    Xv(i) = q(i).(q(1).varName)(q(1).varIndex);
end

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Walter Roberson 2023-11-29

在 MATLAB Online 中打开

Xv = arrayfun(@(IDX) q(IDX).(q(1).varName)(q(1).varIndex), 1:nval);

The assignment is more difficult to arrange.

Jeffrey 2023-12-2

Understood. Thank you.

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Answer 1

Walter Roberson 2023-11-29

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2053437-is-there-a-way-to-perform-this-task-w-o-using-loops#answer_1361892

编辑：Walter Roberson 2023-11-29

The more general vectorized strategy would probably be to set up cell arrays of values, and then use the fact that when you struct() and pass a cell array, then the output is a struct array the size of the cell array.

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Jeffrey 2023-12-2

Understood. I like this answer the best because it's elegant, but will probably stick with the loop instead of introducing cell arrays into my code, to keep it simple.

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Answer 2

Matt J 2023-11-29

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2053437-is-there-a-way-to-perform-this-task-w-o-using-loops#answer_1361897

编辑：Matt J 2023-11-29

在 MATLAB Online 中打开

There are ways to do it without loops, but doing it without loops will be of no benefit to you. It will take more lines of code, consume more memory, and run more slowly.

p.varName = 'L';
p.varIndex = 2;
p.L = [3, 4, 5];
nval = 4;
q = repmat(p,1,nval);
vals = [6 7 8 9];
% Insert values
TMP=vertcat(q.(p.varName));
TMP(:,p.varIndex)=vals;
TMP=arrayfun(@(i)TMP(i,:), 1:nval,'uni',0);
[q.(p.varName)]=deal(TMP{:});
q.L
ans = 1×3
     3     6     5
ans = 1×3
     3     7     5
ans = 1×3
     3     8     5
ans = 1×3
     3     9     5

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Jeffrey 2023-12-2

Understood. Thank you!

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Answer 3

Bruno Luong 2023-11-29

1
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2053437-is-there-a-way-to-perform-this-task-w-o-using-loops#answer_1362072

编辑：Bruno Luong 2023-11-29

在 MATLAB Online 中打开

You might consider store in table instead

NOTE: using table would be more convenient to access data, not necessary faster

p.varName = "L";
p.varIndex = 2;
nval = 4;
q = repmat(p,1,nval);
vals = [6 7 8 9];
% Insert values
for i=1:nval
    q(i).(p.varName)(p.varIndex) = vals(i);
end
T = struct2table(q)
T = 4×3 table
    varName    varIndex      L   
    _______    ________    ______

      "L"         2        0    6
      "L"         2        0    7
      "L"         2        0    8
      "L"         2        0    9
T.varName(1)
ans = "L"
T.(T.varName(1))
ans = 4×2
     0     6
     0     7
     0     8
     0     9
T.(T.varName(1))(:,T.varIndex(1))
ans = 4×1
     6
     7
     8
     9