if(NofGroups == 3 & length(unique(groupdescriptions))==2){
  
  doubleton <- list()
  singleton <- list()
  
  if (groupdescriptions[1] == groupdescriptions[2]) {
     doubleton = c(unique(groupdescriptions[1], groupdescriptions[2]), 
                   groupnames[1], groupnames[2])
     singleton = c(groupdescriptions[3], groupnames[3])
  }  else if (groupdescriptions[2] == groupdescriptions[3]) {
     doubleton = c(unique(groupdescriptions[2], groupdescriptions[3]), 
                   groupnames[2], groupnames[3])
     singleton = c(groupdescriptions[1], groupnames[1])
  }  else {
     doubleton = c(unique(groupdescriptions[1], groupdescriptions[3]),  
                   groupnames[1], groupnames[3])
     singleton = c(groupdescriptions[2], groupnames[2])
  }
}

Given three descriptions, splits them into three variables. Two out of three of these are the same while the other is not: the single set to be compared to the two “identical” sets is emplaced in the singleton list while the other two sets are emplaced in the doubleton list.