Using a string shortcut for nested structure

Question

Jos 2020-1-23

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/501600-using-a-string-shortcut-for-nested-structure

评论： Jos 2020-1-24

采纳的回答： Stephen23

在 MATLAB Online 中打开

Hi all,

I tried using the search function but to no avail. Hopefully you can help me with this one.

Suppose I have a structure called 'tmp':

tmp = struct();
tmp.ahoy.matey = 'hello';

Would it be possible to create a sort of an 'alias' or shortcut using a string to get to 'hello' in a direct way, and also reassign it? I tried:

blah = 'ahoy.matey';
tmp.(blah) = 'hi';

But that gets me an error.

Invalid field name: 'ahoy.matey'.

Sure, I can evaluate it:

eval(['tmp.' blah])
ans =
    'hello'
    
    

But I cannot really change 'hello' into something different.

Is there a way to do this?

Thank you!

Best regards,

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Answer 1

Stephen23 2020-1-23

2
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/501600-using-a-string-shortcut-for-nested-structure#answer_411644

编辑：Stephen23 2020-1-23

在 MATLAB Online 中打开

For accessing a field of one specific structure (which can be nested) you should use dynamic fieldnames:

https://www.mathworks.com/help/matlab/matlab_prog/generate-field-names-from-variables.html

For accessing multiple arbitrary fields of arbitrarily nested structures the most robust way is to use setfield and getfield, for which you will need to split the string into the separate field names (because each field belongs to a different structure, they cannot be provided as one string) which can be provided as a comma-separated list, for example:

>> tmp = struct();
>> tmp.ahoy.matey = 'hello';
>> str = 'ahoy.matey';
>> spl = regexp(str,'\.','split');
>> getfield(tmp,spl{:})
ans = hello
>> tmp = setfield(tmp,spl{:},'world');
>> getfield(tmp,spl{:})
ans = world