MATLAB: Using inputname and varargin for dynamic variable creation (?)

inputnameMATLABprogrammingvarargin

Despite my best programming habits, and in an effort to make my code more modular, I use a couple of places varargin.

Of course, the inputs can vary between each use and I check the names of the variables using inputname() and then load from a .mat file any variables that were not passed in but are needed for the code to run.

But now, I need to use the variables that were passed in that are currently lying in varargin{} — and I need those variable names to be named with what is in inputname{:}…e.g inputname{1}=varargin{1}. I think I could do this with an eval(), but I know that is frowned upon.

I know that [var1, var2, var3]=varargin{:} would work, but the names i need the variables to be called are in inputnams(), and I can't think of how to get this to work.

Is there a good way to get the contents of varargin{} out and into named variables that then lay in the stack?

Thanks!

Best Answer

A couple of options that I can think of:

1. Use assignin. But as you may know, assignin would only allow you to assign to the caller or base workspace. So you can create a function like below, and then call it

assign(inputname(1), varargin{1}).

function assign(varName, varVal)
  assignin('caller', varName, varVal);
end

2. Use a structure:

for id = 1:nargin
  myVar.(inputname(id)) = varargin{id};
end

And change your code so that it uses myVar instead of individual variables.

Related Solutions

MATLAB: Input parsing of name-value Pairs

You could make your own input-parser that searches for a string within varargin, and if it does not exist, ask users. Try the following examples:

Out = exfunction('dog', 'Param1', 10.23, 'Param2', 'cat') %All param-value pairs are defined
Out = exfunction('dog')                                   %Asks user for missing param-value pairs

Here, exfunction uses the parseInputVar to handle param-value pairs and ask users for missing pairs.

function Out = exfunction(arg1, varargin)
  Param1 = parseInputVar('Param1', varargin{:});
  Param2 = parseInputVar('Param2', varargin{:});
  Out = {arg1, Param1 Param2};
function Value = parseInputVar(ParamName, varargin)
  VarLoc = find(strcmpi(varargin, ParamName));
  if ~isempty(VarLoc)
      Value = varargin{VarLoc(1)+1}; %Get the value after the param name
  else
      InputValue = inputdlg(sprintf('What is "%s"?', ParamName));
      Value = sscanf(InputValue{1}, '%f', 1);
      if isempty(Value)
          Value = InputValue{1};
      end
  end

If you want this function to be robust, you could add some more input-checking features into the input parsing function.

MATLAB: Saving a variable from a function with a different name

Simple: call that function with that variable name as its output argument:

var_name = A(X,Y);

will define var_name in the workspace where the function is being called. Passing arguments is the fastest, simplest and neatest way of passing variables between workspaces, and this is what MATLAB themselves recommend (see link below). Whatever you do, do not learn sloppy buggy programing by passing arguments using assignin or globals. Although beginners love using them, actually both of these methods make code slower and buggier.

http://www.mathworks.com/help/matlab/matlab_prog/share-data-between-workspaces.html

The entire concept of functions is very similar to encapsulation, which is broken when you start passing variables willy-nilly in and out of their workspaces. It is a bad idea.

Best Answer

Related Solutions

MATLAB: Input parsing of name-value Pairs

MATLAB: Saving a variable from a function with a different name

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