//   This query assumes range indexes with positions are
//   configured in the database for both xval and yval. It
//   generates some sample data and then performs the
//   aggregation in a separate transaction.

//  Generate data:
declareUpdate();

for (x=1; x<11; x++) {
  var j = 2 * x;
  var o = new Object();
  o.xval = x;
  o.yval = [];
  for (y=0; y<x; y++) { 
    o.yval.push(j);    
  };
  xdmp.documentInsert(("cov" + x + ".json"), o); 
};

*******
// Run the query:
cts.correlation(
  cts.jsonPropertyReference("xval","type=int"),
  cts.jsonPropertyReference("yval","type=int"),
    ["item-frequency"]);
=>
1