Have you ever wondered how MATLAB functions make sense of variable function arguments? Many MATLAB functions take multiple optional arguments, or arguments specified as param-value pairs. A param-value pair is usually supplied with a string parameter name, such as ‘Position’ or ‘Color’ followed by the value of that parameter such as [0 0 1 1] or ‘on’ or some such. You may have seen this paradigm with the graphics functions.<\/p>\n
With the help of the inputParser<\/tt><\/a> class, it’s easy to add param-value pairs to your own functions. This class has two great uses: (1) validation of function inputs and (2) collation of all those inputs into an easy-to-use struct.<\/p>\n InputParser is used in three easy steps:<\/p>\n Create an InputParser<\/strong> Specify All The Inputs<\/strong> Run the Parser on the inputs<\/strong> You can see that the result is a struct with all the inputs broken out into fields. If an optional input was not specified, the default value is placed in the struct.<\/p>\n Use with a function<\/strong> Here we call the function with invalid arguments:<\/p>\n Our validation serves it purpose!<\/p>\n Let us know how if you use inputParser<\/tt> or another method for checking function input.<\/p>\n","protected":false},"excerpt":{"rendered":" Have you ever wondered how MATLAB functions make sense of variable function arguments? Many MATLAB functions take multiple optional arguments, or arguments specified as param-value pairs. A… read more >><\/a><\/p>\n","protected":false},"author":38,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":[],"categories":[69],"tags":[195,192,191,190],"_links":{"self":[{"href":"https:\/\/blogs.mathworks.com\/community\/wp-json\/wp\/v2\/posts\/560"}],"collection":[{"href":"https:\/\/blogs.mathworks.com\/community\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blogs.mathworks.com\/community\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blogs.mathworks.com\/community\/wp-json\/wp\/v2\/users\/38"}],"replies":[{"embeddable":true,"href":"https:\/\/blogs.mathworks.com\/community\/wp-json\/wp\/v2\/comments?post=560"}],"version-history":[{"count":20,"href":"https:\/\/blogs.mathworks.com\/community\/wp-json\/wp\/v2\/posts\/560\/revisions"}],"predecessor-version":[{"id":665,"href":"https:\/\/blogs.mathworks.com\/community\/wp-json\/wp\/v2\/posts\/560\/revisions\/665"}],"wp:attachment":[{"href":"https:\/\/blogs.mathworks.com\/community\/wp-json\/wp\/v2\/media?parent=560"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blogs.mathworks.com\/community\/wp-json\/wp\/v2\/categories?post=560"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blogs.mathworks.com\/community\/wp-json\/wp\/v2\/tags?post=560"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}\n
\n
\nThis step is easy. Just create a new instance.<\/p>\np = inputParser<\/pre>\n
p = \r\n\r\nInput Parser object with:\r\nCaseSensitive: false\r\nStructExpand : true\r\nKeepUnmatched: false\r\nFunctionName : ''<\/pre>\n
\nOnce you have an input parser object, you need to specify each input that you want to parse. In the follow example I add one required, one optional, and one param-value pair parameter. For each input you have to specify a validation function. In these examples I’ve provided an in-line anonymous function or function handle. A handy approve-all function, if you don’t care about validation, is “@(x) true<\/tt>.”<\/p>\n% add required needs the parameter name and a validator anonymous function<\/span>\r\np.addRequired('mainVector'<\/span>,@(x) length(x)>1);\r\n% add optional needs the name, default value, and validator<\/span>\r\np.addOptional('ntimes'<\/span>,1,@isscalar);\r\n% add paramValue needs the parameter name, default value, and validator<\/span>\r\np.addParamValue('title'<\/span>,'Default title'<\/span>,@isstr);<\/pre>\n
\nThe next step is to actually use the inputParser<\/tt> object with a function’s input. In this exmaple example I’m using it to illustrate how the object parses different combinations of inputs.<\/p>\ndisp('parse all options'<\/span>);\r\np.parse([1 2 3 4],2,'title'<\/span>,'mytitle'<\/span>);\r\ninputs = p.Results\r\n\r\n% parse without specifying a title<\/span>\r\ndisp('parse without specifing title param-value pair'<\/span>);\r\np.parse([1 2 3 4], 3);\r\ninputs = p.Results\r\n\r\n%parse with title, no ntimes<\/span>\r\ndisp('parse without optional ntimes'<\/span>);\r\np.parse([5 6 7 8], 'title'<\/span>,'mytitle'<\/span>);\r\ninputs = p.Results<\/pre>\nparse all options\r\n\r\ninputs = \r\n\r\n mainVector: [1 2 3 4]\r\n ntimes: 2\r\n title: 'mytitle'\r\n\r\nparse without specifing title param-value pair\r\n\r\ninputs = \r\n\r\n mainVector: [1 2 3 4]\r\n ntimes: 3\r\n title: 'Default title'\r\n\r\nparse without optional ntimes\r\n\r\ninputs = \r\n\r\n mainVector: [5 6 7 8]\r\n ntimes: 1\r\n title: 'mytitle'<\/pre>\n
\nOf course, the purpose of this is easy input validation and organization within a function. Here’s a sample function and example of validation failure:<\/p>\nfunction<\/span> myfun(input1,varargin)\r\np = inputParser;\r\np.addRequired('mainVector'<\/span>,@(x) length(x)>1);\r\np.addOptional('ntimes'<\/span>,1,@isscalar);\r\np.addParamValue('title'<\/span>,'Default title'<\/span>,@isstr);\r\n\r\np.parse(input1,varargin{:})<\/pre>\nmyfun([1 2 3],[1 2])<\/pre>\n
Error using myfun (line 7)\r\nArgument 'ntimes' failed validation isscalar.<\/pre>\n