Using a string shortcut for nested structure

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,

Answer 1

[Stephen23]

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

See also:

https://www.mathworks.com/help/matlab/matlab_prog/comma-separated-lists.html

https://www.mathworks.com/matlabcentral/answers/320713-how-to-operate-on-comma-separated-lists

TIP: even better than passing around that string would be to just pass the cell array spl.

[Jos]

This is a nice, simple and eloquent way of reffering to nested structs. Many, many thanks!