eval function in for-loop and change of numbers bigger through NaN

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FD 2024-6-9

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评论： Steven Lord 2024-6-10

I have 108 variables with same name but with consecutive numbering. Each of this variables I want to check if there is a value bigger 1000. When yes, then it will be exchanged through NaN.

I try to solve with eval and for-loop, but it doesn't work.

I know the function which changes a value bigger 1000 through NaN.

Function: Temperatur_1(Temperatur_1>1000)=NaN;

Dynamics variabels are: Temperatur_1, Temperatur_2, etc.

eval-function: eval(strcat('Temperatur_',num2str(e)))

for i=1:108

tbd

end

What is the function for checking each variable for > 1000 and saving it in the same variable?

Thank you in advance for your support and solution.

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FD 2024-6-10

I need the single arrays because I'm looking for the minimum and maximum temperature value of each single temperature position. In a matrix is that for my small programming experience not possible. And I have all these arrays in one matrix for another topic.

Steven Lord 2024-6-10

在 MATLAB Online 中打开

A = magic(6)
A = 6x6
    35     1     6    26    19    24
     3    32     7    21    23    25
    31     9     2    22    27    20
     8    28    33    17    10    15
    30     5    34    12    14    16
     4    36    29    13    18    11
<mw-icon class=""></mw-icon>
<mw-icon class=""></mw-icon>
[minValue, minLocation] = min(A, [], 1)
minValue = 1x6
     3     1     2    12    10    11
<mw-icon class=""></mw-icon>
<mw-icon class=""></mw-icon>
minLocation = 1x6
     2     1     3     5     4     6
<mw-icon class=""></mw-icon>
<mw-icon class=""></mw-icon>

In column 4, based on the fourth elements of minValue and minLocation the minimum value of A is 12 and that occurs in row 5.

No need to create A1, A2, A3, A4, A5, and/or A6.

for n = 1:width(A)
    fprintf("In column %d of A, the minimum value is %d" + ...
        " and this occurs at (%d, %d).\n", n, minValue(n), minLocation(n), n)
end
In column 1 of A, the minimum value is 3 and this occurs at (2, 1).
In column 2 of A, the minimum value is 1 and this occurs at (1, 2).
In column 3 of A, the minimum value is 2 and this occurs at (3, 3).
In column 4 of A, the minimum value is 12 and this occurs at (5, 4).
In column 5 of A, the minimum value is 10 and this occurs at (4, 5).
In column 6 of A, the minimum value is 11 and this occurs at (6, 6).

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Answer 1

Matlab Pro 2024-6-10

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https://ww2.mathworks.cn/matlabcentral/answers/2126856-eval-function-in-for-loop-and-change-of-numbers-bigger-through-nan#answer_1469476

在 MATLAB Online 中打开

Hi @Franziska

I simply combine your inputs to a simple code (with indexes 1-->4):

Please re-conider @Stephen23 comments

Temperatur_1 = 500;
Temperatur_2 = 300;
Temperatur_3 = 1001;
Temperatur_4 = 3;
suffixes = num2cell(1:4);
for i =1:4
    vName = sprintf('Temperatur_%d',i);
    eval(sprintf('%s(%s>1000) = NaN',vName,vName))
end

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FD 2024-6-10

Perfect. It works. Big thank you!!

Stephen23 2024-6-10

You should read this:

https://www.mathworks.com/matlabcentral/discussions/tips/849901-tutorial-why-variables-should-not-be-named-dynamically-eval/2593476

and also what the MATLAB documentation states about your data design: "A frequent use of the eval function is to create sets of variables such as A1, A2, ..., An, but this approach does not use the array processing power of MATLAB and is not recommended. The preferred method is to store related data in a single array. If the data sets are of different types or sizes, use a structure or cell array."

source: https://www.mathworks.com/help/matlab/matlab_prog/string-evaluation.html

Better data design would make your code simpler and more efficient.

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eval function in for-loop and change of numbers bigger through NaN

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