check dimensions for parameters

Hello, in a current setup I very often load datasets from an m file and write over current variables in the base workspace. My problem is that sometimes the dimensions differ and I then get problems with my simulations. Lets say I have a variable a = 1 in my workspace and then try to write a = [1 1; 1 1] from my m file. In that case I would like to cancel that and inform the user that there was a dimension mismatch for that variable. I tried some quite complicated way might work by using eval and evalin but there must be an easier way to fix that...can someone help me?

[Stephen23]

Avoid using eval, evalin, assignin, etc. They will only cause problems. Write functions, and pass the arguments properly. Checking input arguments is then trivial.

Guillaume's answer and explanation is spot on.

Answer 1

[Guillaume]

The answer is to change the way you work and rewrite your script as a function. Instead of dumping your dataset into the base workspace you would pass these inputs to your function, which in the first step would simply validate the inputs and issue an error message if they're the wrong shape.

For validating inputs, you can use validateattributes:

function [possibleoutput] = usedtobescript(a, b, c) %use better variable names
    validateattributes(a, {'numeric'}, {'scalar'}); %issues an error if a is not numeric or scalar
    %...
end

[Marlo Wegener]

Hej thanks for the answer, I'm actuall wrote a script for that and used the code below...not exactly as you recommended...

dimensionError = {};
VariableInWorkspace = 1;
for i = 1:length(newData)
    try
        existingValue = evalin('base', newData{i});
        existingValueSize = numel(existingValue);
    catch
        VariableInWorkspace = 0;
    end
    newValue = eval(newData{i});
    newValueSize = numel(newValue);
    if existingValueSize == newValueSize &&  VariableInWorkspace == 1
        assignin('base', newData{i}, newValue);
    elseif VariableInWorkspace == 0
        assignin('base', newData{i}, newValue);
        VariableInWorkspace = 1;
    else
        dimensionError{end+1,1} = newData{i};
    end
end

but then I get problems using assignin

[Marlo Wegener]

I also have to filter out all names as I have structures of different size as e.g. A.Ag.C.var1, A.Ag.D.var2, A.Cd.T.var3 and so on

[Guillaume]

As I said, use functions not scripts. And above all, do not use assignin, evalin, eval and co. They're not recommended for a reason. They cause more problem than they solve.

Use function inputs and outputs to pass variables between different pieces of code. It's much cleaner and it's easier to keep track of what is what. A function should not read or write variables in the base workspace.

As an aside, since scripts share the base workspace, there is no reason for a script to use evalin or assignin. The script can access the variable directly.