How to deal with name/value pairs of function arguments in MATLAB

Question

I have a function that takes optional arguments as name/value pairs.

function example(varargin) % Lots of set up stuff vargs = varargin; nargs = length(vargs); names = vargs(1:2:nargs); values = vargs(2:2:nargs);  validnames = {'foo', 'bar', 'baz'};     for name = names    validatestring(name{:}, validnames); end  % Do something ... foo = strmatch('foo', names); disp(values(foo)) end  example('foo', 1:10, 'bar', 'qwerty') 

It seems that there is a lot of effort involved in extracting the appropriate values (and it still isn't particularly robust again badly specified inputs). Is there a better way of handling these name/value pairs? Are there any helper functions that come with MATLAB to assist?

Answer 1

I prefer using structures for my options. This gives you an easy way to store the options and an easy way to define them. Also, the whole thing becomes rather compact.

function example(varargin)  %# define defaults at the beginning of the code so that you do not need to %# scroll way down in case you want to change something or if the help is %# incomplete options = struct('firstparameter',1,'secondparameter',magic(3));  %# read the acceptable names optionNames = fieldnames(options);  %# count arguments nArgs = length(varargin); if round(nArgs/2)~=nArgs/2    error('EXAMPLE needs propertyName/propertyValue pairs') end  for pair = reshape(varargin,2,[]) %# pair is {propName;propValue}    inpName = lower(pair{1}); %# make case insensitive     if any(strcmp(inpName,optionNames))       %# overwrite options. If you want you can test for the right class here       %# Also, if you find out that there is an option you keep getting wrong,       %# you can use "if strcmp(inpName,'problemOption'),testMore,end"-statements       options.(inpName) = pair{2};    else       error('%s is not a recognized parameter name',inpName)    end end 

Answer 2

InputParser helps with this. See Parse Function Inputs for more information.