Accessing the string elements

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pradeep kumar 2017-10-17

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/361781-accessing-the-string-elements

编辑： Cedric 2017-10-17

采纳的回答： Cedric

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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 2017-10-17

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

Stephen23 2017-10-17

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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采纳的回答

Cedric 2017-10-17

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/361781-accessing-the-string-elements#answer_286240

编辑：Cedric 2017-10-17

在 MATLAB Online 中打开

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