// This macro demonstrates how to use the
// RoiManager.setGroup(), RoiManager.selectGroup()
// and RoiManager.selected macro functions.
// It creates a stack with many ROIs in the ROI Manager
// and then combines all the ROIs in each individual
// slice into one. It requires ImageJ 1.53e.

 // create a stack
  size = 500;
  slices = 50;
  setBatchMode(true);
  newImage("Untitled", "8-bit black", size, size, slices);
  roiManager("reset");

  // adds ROIs, in groups, to the ROI Manager
  for (i=0; i<slices*10; i++) {
     x = random*0.6*size;
     y = random*0.6*size;
     makeOval(x, y, 0.3*size, 0.3*size);
     Roi.setGroup(round(1+random*(slices-1)));
     roiManager("Add");
  }

  // select the ROIs in each grounp and combine them 
  for (i=1; i<=nSlices; i++) {
     RoiManager.selectGroup(i);
     if (RoiManager.selected()>0) {
        roiManager("Combine");
        Roi.setPosition(i);
        roiManager("Add");
        roiManager("delete");
     }
  }
  Roi.remove;
  run("From ROI Manager");
  setBatchMode(false);
  run("Animation Options...", "speed=3 start");