The 'index' output parameter in CALL SORTNDX is not assigned an element size. Therefore, if you reassign the vector to a new vector, the values are lost and assigned to zeroes.

The problem is illustrated in this example:

       proc iml;
          m = { 1 1 0, 
                2 0 0, 
                1 3 1, 
                2 2 2 }; 
          call SORTNDX(index, m, {1 3}, {3} ); 
          newindex = index; 
          print index newindex; 
        quit; 

To circumvent the problem, initialize the 'index' output parameter before issuing the call:

       proc iml;
          m = { 1 1 0, 
                2 0 0, 
                1 3 1, 
                2 2 2 }; 
          index=0;
          call SORTNDX(index, m, {1 3}, {3} ); 
          newindex = index; 
          print index newindex; 
        quit; 

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