//////////////////////////////////////////////
double NA=0/0;                 //Missing value constant
range rA=[Book1]Sheet1!col(A); //Data range for col(A) in Sheet1 in Book1
rA=sort(rA);                   //Sort the range of column A
range rT=[??]!_tmpdata;        //Range for temporary dataset
int nirows=rA.getSize();       //Number of input rows
int norows=0;                  //Number of output rows
for(ii=1; ii<=nirows; ii=ii+1) { //Loop over with ii
  if(ii==1 || rA[ii]!=rA[ii-1]) {
    rT[ii]=rA[ii];   //If 1st row, or unequal to previous row, set the same
    norows=norows+1; //Increment number of output rows
  }
  else rT[ii]=NA;    //Otherwise set a missing value
}
rA=sort(rT);         //Put the sorted temp dataset back
rA.setSize(norows);  //Reset the size of column A
/////////////////////////////////////////////