How to create new structure with each for loop?

Question

Nicholas Kavouris 2022-4-10

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1692865-how-to-create-new-structure-with-each-for-loop

评论： Stephen23 2022-4-10

I am trying to take a large dataset with mutlple fields and segment it and place it into unique structure with each for loop

if numel(start)==numel(stop)
    for k=1:numel(start);
        j=start(k):stop(k)+900;
        field1="number"; value1=k;
        field2='grill_state'; value2=grill_state(j) ;
        field3='Set_Temp'; value3=SetTempF(j);
        field4='TempF'; value4=Temp_F(j);
        field5='AugerRPM'; value5=Auger_RPM(j);
        strcat('Cook',num2str(k))=struct(field1,value1,field2,value2,field3,value3,field4,value4,field5,value5);
    end
end

The goal is to take all values indexed between start and stop and place them into a structure titled Cookn for 1-n number of cooks.

so if there are 5 start points then loop should return struct cook1-cook5. Where am i going wrong?

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Stephen23 2022-4-10

"Where am i going wrong?"

You are trying to force numbers into variable names.

Doing so is possible, but only if you want to write slow, complex, inefficient, buggy code:

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

The neat, simple, and very efficient MATLAB approach is to use indexing, just as Matt J shows.

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Answer 1

Matt J 2022-4-10

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https://ww2.mathworks.cn/matlabcentral/answers/1692865-how-to-create-new-structure-with-each-for-loop#answer_938970

在 MATLAB Online 中打开

if numel(start)==numel(stop)
    
    N=numel(start);
    
    clear Cook
    for k=N:-1:1
        
        j=start(k):stop(k)+900;
        Cook(k).number=k;
        Cook(k).grill_state=grill_state(j) ;
        Cook(k).Set_Temp=SetTempF(j);
        Cook(k).TempF=Temp_F(j);
        Cook(k).AugerRPM=Auger_RPM(j);
        
       end
end

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Nicholas Kavouris 2022-4-10

thank you, much simpler. Any reason for backwards loop?

Matt J 2022-4-10

You're quite welcome, but please Accept-click the answer if it resolved your question.

The backward loop forces Matlab to create the Nth structure array element first. As a result, it forces the entire structure array to be pre-allocated after the first iteration of the loop.

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