MATLAB: Making new objocts out of the content of a cell vector

cell vectorMATLAB

Hello!

I am everything else than an expert in Matlab, but I hope that my explanation still makes sense to you. My problem is the following:

I have a vector that looks like this:

B = {'USA' 'GER' 'JAP'…}'; (it is actually 110 country codes

now I want to assign each country code a number like: USA = 1; GER = 2; JAP = 3; … (keeping the same order as in the vector)

Is there a quick way of doing this?? I would be very glad if I don't have to write 110 country codes by hand!

Thaaaaank you very much!!

Best Answer

It sounds like you might want to use a containers.Map object.

doc containers.Map

And an example:

cm = containers.Map({'USA';'GER';'JAP'},[1;2;3]);

And a sanity check, is 'USA' number 1?

cm('USA')

You betcha!

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MATLAB: Loop concerning workspace names

Way to go in answering your own question and not giving anybody else a chance to offer a different option!

This is completely the wrong approach! You're now going to have tons of eval in your code, making it slow (the content of the eval can't be optimised by matlab), hard to debug (mlint can't highlight errors in the eval, you can't step through the eval code) and more complicated than it needs to be

Much, much better would be to change the way you actually store your data. Do not embed metadata in a variable names. Instead of having a separate variable for each nation, use a single variable for all and an index to access each nation. Two easy options: containers.Map or table. Example using a map:

%first, getting rid of all those variables:
CountryNames = {'USA'; 'MEX'; 'ESP'};
CountryPopulation = containers.Map;
for countryidx = 1:numel(CountryNames)
   CountryPopulation(CountryNames{countryidx}) = eval([CountryNames{countryidx}, 'population']);
end
%calculate the ratioed countries population
%No need for eval anymore
MeanRatioPopulation = containers.Map(CountryPopulation.keys, cellfun(@(pop) pop / 2, CountryPopulation.values, 'UniformOutput', false);

MATLAB: Accessing the string elements

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

Best Answer

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MATLAB: Accessing the string elements

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