Help on selection sort function

I have put together the ssort function below that takes in two arguments; one array that gets sorted and an argument ('up', 'down') that tells the function to sort in ascending('up') or descending('down') order. For example ssort([5 7 2 12 6],'up') sorts the array in the argument in ascending order.

I am trying to make it so that even if the second argument is never entered, the input array will default to being sorted in ascending order. Unfortunately in my code below, I have only managed to default to sorting for ascending order for ssort([5 7 2 12 6], ' ') which is not the same as running ssort([5 7 2 12 6]) which is what I am looking to accomplish. When I attempt to run ssort([5 7 2 12 6]), I get an error telling me that I have too few input arguments. Any insight would be extremely appreciated.

function out = ssort(a,b)
%SSORT Selection sort data; data may be sorted in ascending or descending order
%Function SSORT sorts a numeric dataset into desired order. 

narginchk(1,2);

nvals=size(a,2);

if nvals==0 || nvals==1
   msg='You have not entered a proper array for sorting';
   error(msg);
end

for ii=1:nvals-1
   iptr=ii;
  for jj=ii+1:nvals
        if strcmp(b,'up')==1 
           if a(jj)>a(iptr)
              iptr=jj;
           end
        elseif strcmp(b,'down')==1 || isempty(b)==1
           if a(jj)<a(iptr)
              iptr=jj;
           end
        else
            k='Invalid sorting option!';
            error(k);
        end
  end  
  if ii~=iptr
       temp = a(ii);
       a(ii) = a(iptr);
       a(iptr) = temp;
  end
end

out=a;

[the cyclist]

Is there a reason you are not just using the built-in sort function, as provided by MATLAB? Is this a homework assignment to write your own sort?

[Maroulator]

Correct; this is a homework assignment that requires me to write my own sort function.

Answer 1

[the cyclist]

Trying putting these lines just after you check the number of arguments:

if nargin < 2
    b = 'up'
end

Also, 'up' seems to sort in what is normally called descending order (from highest value down to lowest). Is that what you intended?

Answer 2

[Image Analyst]

function out = ssort(a,b)
if nargin == 1 || lower(b(1)) == 'u'
    out = sort(a, 'Ascend');
else
    out = sort(a, 'Descend');
end