How to insert a int value into the name of a variable (for loop)

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Duncan Wright 2017-9-1

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评论： Duncan Wright 2017-9-1

I'm trying to iterate throw these variable names in a for loop, here's my code:

form= 'dd-mmm-yyyy HH:MM:SS';
for i = 1:15
    yearfrac=vpa(string([data_v3_data.b [INSERT i here] date]),10);
    year = double(fix(yearfrac))
    day = double(yearfrac-year)
    a = datestr(datenum(year,1,1)+day*365)
    data_v3_data.b + [INSERT i here] + date = datenum(a,form)
end

[INSERT i here] indicates where I would like the integer (1:15) to appear. I have a list of variables named:

data_v3_data.b1date
data_v3_data.b2date
data_v3_data.b3date
data_v3_data.b4date
etc etc..

Thanks !

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Adam 2017-9-1

Just use arrays and indexing. why use 15 variables when 1 will do?!

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

Stephen23 2017-9-1

编辑：Stephen23 2017-9-1

在 MATLAB Online 中打开

[INSERT i here]

tells us that you want an index. So why not use a real indexing instead of trying to write slow complicated code and pointlessly forcing meta-data (the index) into some names?

Indexing is fast and very efficient. Use it.

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Answer 1

Stephen23 2017-9-1

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编辑：Stephen23 2017-9-1

在 MATLAB Online 中打开

Just use a non-scalar structure:

data(1).date = ...
data(2).date = ...
data(3).date = ...
data(4).date = ...

This makes it trivially easy to access the data using indexing, which is fast and efficient, e.g. the second date:

data(2).date

Not only that you can very conveniently convert any field into a comma-separated list, which makes it simple to join the field values together into one array, e.g. to put all the dates into one cell array:

out = {data.date}

or to assign them in exactly the same way.

While it is possible to define structure fieldnames dynamically, in your case (you proposed numbered field names) it serves no purpose whatsoever and will only make your code slow and complicated.

Writing neat efficient MATLAB code is easy, once you avoid bad design decisions like putting meta-data into field or variable names:

https://www.mathworks.com/matlabcentral/answers/228557-experts-of-matlab-how-did-you-learn-any-advice-for-beginner-intermediate-users

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