MATLAB: HOW TO CHECK THE PARAMETERS RECEIVED IN THE FUNCTION CALL

functionparseinput

dear all,

this is my function : function [] = print( value1 , value2, value3 ,value4,value5,value6,value7,value8)

value1 and value 2 are REQUIRED the others are OPTIONAL . I need to know how to check which parameters i've received and their value , because some of them could be numbers , characters . and i don't know how to do that. thanks

Best Answer

I think input parser + varargin is what you need here.

Example:

%Changed the name "print" to "print2" to prevent overriding matlab built-in "print" function
function [] = print2(varargin)  
P = inputParser;
addRequired(P, 'value1', @ischar);
addRequired(P, 'value2', @isnumeric);
addOptional(P, 'value3', [], @(x) ischar(x) || isnumeric(x));
parse(P, varargin{:});
P = P.Results; %Just so you can refer to value1 as P.value1, not P.Results.value1 (downside to inputParser)
%To get value1, use P.value1

Alternatively, you'll have to make your own input-parsing function

Related Solutions

MATLAB: Check if a number of varibles in a function satifies a condition.

There are already tools for performing these tasks. Check out the InputParser class [ ref, ref ]. It will allow you to declare three sets of arguments: required, optional, and param/value pairs. For each parameter, you will be able to define a check function, as well as a default value for all but required parameters.

EDIT: just as an example, here is the beginning of a function using an input parser

 function [hFig, hAxis, hLegend, hPatches] = bar_varWidth( colWidth, ...
    data, varargin )
    % --- 1. Parse input parameters.
    parser = inputParser ;
    parser.StructExpand  = true ;
    parser.CaseSensitive = false ;
    parser.addRequired( 'colWidth', @isnumeric ) ;
    parser.addRequired( 'data', @isnumeric ) ;
    parser.addParamValue( 'legend', [], @(x) ischar(x) || iscell(x)  ) ;
    parser.addParamValue( 'xTickLabel', [], @(x) isnumeric(x) || iscell(x)  ) ;
    parser.addParamValue( 'xTickLabelFormat', '%.2f', @ischar ) ;
    parser.addParamValue( 'xTickLabelShiftThreshold', 10, @isnumeric ) ;
    parser.addParamValue( 'xTickLabelAngle', 90, @isnumeric ) ;
    parser.addParamValue( 'xTickLabelLineLength', [], @isnumeric ) ;
    parser.parse( colWidth, data, varargin{:} ) ;
    args = parser.Results ;
    % --- 2. ...

and here all parameters are accessible as fields of args, e.g.

    args.colWidth
    args.legend

MATLAB: Possible bug in Parse function input

This does seem to be a limitation in the implementation of inputParser. Following code show a case where the parser will fail. In this code, the second optional input is a char array.

function a = findArea(width, varargin)
   defaultHeight = 1;
   defaultUnits = 'inches';
   defaultShape = 'rectangle';
   expectedShapes = {'square','rectangle','parallelogram'};
   p = inputParser;
   validScalarPosNum = @(x) isnumeric(x) && isscalar(x) && (x > 0);
   validScalarPosNum2 = @(x) ischar(x); % <---- the optional parameter is char array
   addRequired(p,'width',validScalarPosNum);
   addOptional(p,'height',defaultHeight,validScalarPosNum2);
   addParameter(p,'units',defaultUnits,@isstring);
   addParameter(p,'shape',defaultShape,...
                 @(x) any(validatestring(x,expectedShapes)));
   parse(p,width,varargin{:});
   
   a = p.Results; 
end

now call it like this

>> findArea(7, 'shape', 'square')
Error using findArea (line 14)
No value was given for 'square'. Name-value pair arguments require a name
followed by a value.

I skipped the optional parameter height, but the parser failed to note that.

I guess this is done intentionally by MATLAB to avoid some kind of ambiguity in parsing the inputs. For example, in this case, it is easy to tell since we are using a single optional input. But consider a function that takes several optional inputs and parameters. In that case, it will become difficult for the parser to guess which values are optional inputs and which are parameters.

Note that the parser will only fail if you are taking character array as inputs for optional parameters. I guess the MATLAB expects that the character arrays should be input using parameters.

Best Answer

Related Solutions

MATLAB: Check if a number of varibles in a function satifies a condition.

MATLAB: Possible bug in Parse function input

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