Question

In Matlab when one tries to access an element of a matrix that doesn’t exist usually an error is raised:

>> month(0)
??? Subscript indices must either be real positive integers or logicals.

I was wondering whether there is a function that allows supplying default value in such cases. E.g.,:

>> get_def(month(0), NaN)
ans =
   NaN

P.S. I can workaround this particular case of subscript (0), but I was wondering about more generic way of doing this.

Answer 1

There is no built-in MATLAB function to do what you want. You could use a try-catch block:

>> try a = month(0); catch a = nan; end
>> a

a =

   NaN

However, the best option would probably be to error-check the index first, throwing an error or setting a variable to a default value if it is out of range.

If you really want to try using an index that may be 0, you could write your own get_def function. Here’s one way to do it:

function value = get_def(vector,index,defaultValue)
  try
    value = vector(index);
  catch
    value = defaultValue;
  end
end

You would then use this function in the following way:

>> month = 1:12;
>> get_def(month,0,nan)

ans =

   NaN

>> get_def(month,1,nan)

ans =

     1