Accessing the string elements

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pradeep kumar le 17 Oct 2017

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Modifié(e) : Cedric le 17 Oct 2017

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I have 3 strings like the following:

world=["America", "Europe"]; % Parent String 
America=["USA", "Brazil", "Argentina"]; % Child1 String 
Europe=["France", "Germany", "England"]; % Child2 String

I want to access the elements of the child string (Country names) from the Parent string(world) and use it inside a for loop for further operation. I am trying in the following way:

for i=1:2
  d=world(i); % Temporary variable to store the continent name
for j=1:3
disp(d(j)); % Throws an Error: "Index exceeds Matrix dimensions
end
end

What am I doing wrong? Any help will be highly appreciated.

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KL le 17 Oct 2017

You're defining three entirely different variables. Where and how do you want to apply this?

Stephen23 le 17 Oct 2017

The simplest and most efficient solution is to use structures and dynamic fields:

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

Do not try to magically access variable names. Doing so will make your code slow, complex, buggy, hard to debug, inscure. Read this to know why:

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

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Cedric le 17 Oct 2017

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Here is one way, as string arrays are "iterable".

continents = ["America", "Europe"] ; 
countries.America = ["USA", "Brazil", "Argentina"] ;
countries.Europe  = ["France", "Germany", "England"] ;
for continent = continents
    fprintf('%s :\n', continent ) ;
    for country = countries.(continent)
        fprintf('\t%s\n', country) ;
    end
end

Yet, using dynamic field names for that is usually not advised. You could use cell arrays instead:

continents = {"America", "Europe"} ; 
countries{1} = {"USA", "Brazil", "Argentina"} ;
countries{2} = {"France", "Germany", "England"} ;
for continentId = 1 : numel( continents )
    fprintf('%s :\n', continents{continentId} ) ;
    for countryId = 1 : numel( countries{continentId} )
        fprintf('\t%s\n', countries{continentId}{countryId} ) ;
    end
end