Passing varargs to plot() function

Question

I am writing a wrapper for plot that automates some tasks that I find myself doing frequently.

An example code snippet might look like

function myplot(x,y,varargin)
    plot(x,y,varargin{:})
    xlabel('x axis')
    ylabel('y axis')
end

I'm using Matlab's varargin to pass additional arguments to plot. However, I find that I might want to pass my own optional arguments in varargin. For example, I might want to write something like

>> myplot(1:10, 1:10, 'r', 'LineWidth', 2, 'legend', {'Series 1'})

to have the function automatically include a legend in the plot - that is, I want to be able to mix my own keyword arguments with the ones that you can supply to plot. Short of writing a full parser for my varargs, is there a way to do this simply and reusably in Matlab?

I've tried to use the inputParser object, but that would require me to manually add every possible additional argument to plot (and a default for it) which doesn't seem ideal.

Answer 1

inputParser may still be the best choice. You can construct the object for your additional arguments, and lump all the parameterName/parameterValue pairs that you want to pass to plot into Unmatched.

function myplot(x,y,varargin)

    parserObj = inputParser;
    parserObj.KeepUnmatched = true;
    parserObj.AddParamValue('legend',false); 
    %# and some more of your special arguments

    parserObj.parse(varargin);

    %# your inputs are in Results
    myArguments = parserObj.Results;

    %# plot's arguments are unmatched
    tmp = [fieldnames(parserObj.Unmatched),struct2cell(parserObj.Unmatched)];
    plotArgs = reshape(tmp',[],1)'; 


    plot(x,y,plotArgs{:})
    xlabel('x axis')
    ylabel('y axis')

    if myArguments.legend
       %# add your legend
    end
end

Answer 2

To support the Linespec argument without interfering with input parser parameters that have a name of 4 characters or less (e.g., 'grid' or 'bins'), you should have a slightly more sophisticated way to check the validity of the Linespec argument than '@(x) ischar(x) && numel(x) <=4'. This check would return true also for 'grid' and 'bins', although they are no valid Linespec arguments.

The following function will return true only if a valid Linespec argument is entered:

function isls = islinespec(x)
isls    = false;

if ~ischar(x)
    return;
end

lineStyleSpecifiers     = {'--','-.','-',':'};
markerSpecifiers        = {'square','diamond','pentagram','hexagram','+','o','*','.','x','s','d','^','v','>','<','p','h'};
colorSpecifiers         = {'r','g','b','c','m','y','k','w'};

for oo=1:length(lineStyleSpecifiers)
    k = strfind(x,lineStyleSpecifiers{oo});
    if ~isempty(k)
        x(k:(k+length(lineStyleSpecifiers{oo})-1)) = [];
        break;
    end
end

for oo=1:length(markerSpecifiers)
    k = strfind(x,markerSpecifiers{oo});
    if ~isempty(k)
        x(k:(k+length(markerSpecifiers{oo})-1)) = [];
        break;
    end
end

for oo=1:length(colorSpecifiers)
    k = strfind(x,colorSpecifiers{oo});
    if ~isempty(k)
        x(k:(k+length(colorSpecifiers{oo})-1)) = [];
        break;
    end
end

if isempty(x)
    isls = true;
end

(Admittedly, the function could have been written more elegantly with regular expressions, but it does the trick.)

Example usage:

parserObj = inputParser;
parserObj.KeepUnmatched = true;
parserObj.AddParamValue('legend',false);
parserObj.AddParamValue('grid',true);
parserObj.addOptional('LineSpec','-', @(x) islinespec(x));