CODEWITHSUNDEEP
matlab
Sam Roberts
Sam Roberts

Reputation: 24127

Implementing multiple syntaxes for a MATLAB plot function

Many of the plotting functions in MATLAB and toolboxes (thought not all) allow both the following syntaxes:

plotfcn(data1, data2, ...)
plotfcn(axes_handle, data1, data2, ...)

The first plots into the current axes (gca) or creates and plots into a new axes if none exists. The second plots into the axes with handle axes_handle.

Having looked into the internals of several MATLAB and toolbox plotting functions, it looks like there isn't really a standardised way that MathWorks do this. Some plotting routines use the internal, but open, function axescheck to parse the input arguments; some do a simple check on the first input argument; and some use a more complex input-parsing subfunction that can handle a larger variety of input syntaxes.

Note that axescheck appears to use an undocumented syntax of ishghandle - the doc says that ishghandle takes only one input, returning true if it is any Handle Graphics object; but axescheck calls it as ishghandle(h, 'axes'), which returns true only if it's specifically an axes object.

Is anyone aware of a best practice or standard for implementing this syntax? If not, which way have you found to be most robust?

Upvotes: 1

Views: 248

Answers (3)

Sam Roberts
Sam Roberts

Reputation: 24127

In case anyone is still interested, four years after I posted the question, this is the pattern that I have mostly settled on.

function varargout = myplotfcn(varargin)
% MYPLOTFCN Example plotting function.
%
% MYPLOTFCN(...) creates an example plot.
%
% MYPLOTFCN(AXES_HANDLE, ...) plots into the axes object with handle
% AXES_HANDLE instead of the current axes object (gca).
%
% H = MYPLOTFCN(...) returns the handle of the axes of the plot.

% Check the number of output arguments.
nargoutchk(0,1);

% Parse possible axes input.
[cax, args, ~] = axescheck(varargin{:});

% Get handle to either the requested or a new axis.
if isempty(cax)
    hax = gca;
else
    hax = cax;
end

% At this point, |hax| refers either to a supplied axes handle,
% or to |gca| if none was supplied; and |args| is a cell array of the
% remaining inputs, just like a normal |varargin| input.

% Set hold to on, retaining the previous hold state to reinstate later.
prevHoldState = ishold(hax);
hold(hax, 'on')          


% Do the actual plotting here, plotting into |hax| using |args|.


% Set the hold state of the axis to its previous state.
switch prevHoldState
    case 0
        hold(hax,'off')
    case 1
        hold(hax,'on')
end

% Output a handle to the axes if requested.
if nargout == 1
    varargout{1} = hax;
end

Upvotes: 1

Dennis Jaheruddin
Dennis Jaheruddin

Reputation: 21563

Two recommendations from the sideline:

  1. Don't go undocumented if you don't need to.
  2. If a simple check is sufficient, this would have my personal preference.

Upvotes: 0

memyself
memyself

Reputation: 12638

not sure I understand the question. What I do is to separate the plotting of data from the generation / setup of plots. So if I want to plot a histogram in a standardized way I have a function called setup_histogram(some, params) which will return the appropriate handles. Then I have a function update_histogram(with, some, data, and, params) which will write the data into the appropriate handles.

This works very well, if you have to plot lots of data the same way.

Upvotes: 0

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