mapreduce.js

map = function(){
  this.log.forEach(function(logItem){
    if(logItem.action == 'Call' && logItem.user != ''){
      emit({user: logItem.user, time:logItem.time}, 1);
    }
  });
};

reduce = function(key, values){
  return values;
};

db.leads.mapReduce(map, reduce, {out:'leadCallsReduce'});

{
    "result" : "leadCallsReduce",
    "timeMillis" : 1012,
    "counts" : {
        "input" : 5951,
        "emit" : 7804,
        "reduce" : 0,
        "output" : 7804
    },
    "ok" : 1,
}