Using a string variable as a variable name in an equation.

Question

Jaxson Bonsall 2023-11-20

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2049932-using-a-string-variable-as-a-variable-name-in-an-equation

编辑： Stephen23 2023-11-21

Hello this is my current code which works fine but I want the second portion to be more automated. The main thing I am unsure of here is how to use a cell value from a vector of strings as a variable name in an equation later on.

Plex_Nms = [{'ELEC'}; {'FO'}; {'HVAC'}];
Diff_Value = 3;
ELEC    = [61 62 64 65 67 68 70 71 21 24]';                              
FO      = [16 60 63 66 69]';                                                
HVAC    = [16 60 63 66 69 182]';

Currently the only way I can get my code to operate is using the 3 lines below but I would rather do this in a for loop.

Plex_Add_VCs{1} = ELEC - Diff_Value;
Plex_Add_VCs{2} = FO - Diff_Value;
Plex_Add_VCs{3} = HAVC - Diff_Value;

I would like it to worklike this instead of the 3 lines above but the for loop does not work.

for i = 1:3
    Plex_Add{i} = Plex_Nms(i) - Diff_Value;
end

I am unsure of how to get Plex_Nms(i) to act as if I am using the ELEC variable name.

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Stephen23 2023-11-21

编辑：Stephen23 2023-11-21

"The main thing I am unsure of here is how to use a cell value from a vector of strings as a variable name in an equation later on."

Accessing variable names like that is one way that users force themselves into writing slow, complex, inefficient, insecure, fragile, obfuscated code that is buggy and hard to debug. Best avoided.

Use a container array, e.g. structure, table, cell array. Then use indexing. Indexing is simple and efficient.

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Answer 1

Sulaymon Eshkabilov 2023-11-20

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在 MATLAB Online 中打开

If understood your question correctly, is this what you are trying to solve for:

Diff_Value = 3;
ELEC    = [61 62 64 65 67 68 70 71 21 24]';                              
FO      = [16 60 63 66 69]';                                                
HVAC    = [16 60 63 66 69 182]';
Plex_Nms = [{ELEC}, {FO}, {HVAC}];
Plex_Add_VCs{1} = ELEC - Diff_Value;
Plex_Add_VCs{2} = FO - Diff_Value;
Plex_Add_VCs{3} = HVAC - Diff_Value;
for i = 1:3
    Plex_Add{i} = Plex_Nms{i} - Diff_Value;
end
% To display/see the found solutions
celldisp(Plex_Add)
 
Plex_Add{1} =
 
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Plex_Add{2} =
 
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Plex_Add{3} =
 
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Jaxson Bonsall 2023-11-20

No thats not what I am trying to do. I am trying to use the for loop instead of the 3 lines above that to do the same thing but the for loop does not work because the equation in the for loop does not recognize Plex_Nms{i} as ELEC, FO, or HVAC so that those vectors can be used in the equation.

Voss 2023-11-20

在 MATLAB Online 中打开

I think it works. Just remove those three lines you don't need.

Diff_Value = 3;
ELEC    = [61 62 64 65 67 68 70 71 21 24]';                              
FO      = [16 60 63 66 69]';                                                
HVAC    = [16 60 63 66 69 182]';
Plex = {ELEC; FO; HVAC};
Plex_Add = cell(size(Plex));
for i = 1:numel(Plex)
    Plex_Add{i} = Plex{i} - Diff_Value;
end
% To display/see the found solutions
celldisp(Plex_Add);
 
Plex_Add{1} =
 
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Plex_Add{2} =
 
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Plex_Add{3} =
 
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   179

 

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Answer 2

Voss 2023-11-20

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2049932-using-a-string-variable-as-a-variable-name-in-an-equation#answer_1356822

在 MATLAB Online 中打开

You can put those vectors into a struct, using their names as fields:

Plex_Nms = {'ELEC'; 'FO'; 'HVAC'}; % names
ELEC    = [61 62 64 65 67 68 70 71 21 24]';                              
FO      = [16 60 63 66 69]';                                                
HVAC    = [16 60 63 66 69 182]';
Plex_Vls = {ELEC; FO; HVAC};       % values
% create a struct S:
args = [Plex_Nms Plex_Vls].';
S = struct(args{:});
disp(S);
    ELEC: [10×1 double]
      FO: [5×1 double]
    HVAC: [6×1 double]

Then create a new struct with the same fields and decrease the values by Diff_Value:

Diff_Value = 3;
S_new = S;
fn = fieldnames(S);
for ii = 1:numel(fn)
    S_new.(fn{ii}) = S.(fn{ii}) - Diff_Value;
end
disp(S_new);
    ELEC: [10×1 double]
      FO: [5×1 double]
    HVAC: [6×1 double]
disp(S_new.ELEC);
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disp(S_new.FO);
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disp(S_new.HVAC);
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