map-reduce-example

map = function() {
  emit(this.suit,{count:1});
}

reduce = function(key, values) {
  var total = 0;
  for ( var i=0; i<values.length; i++ )
    total += values[i].count;
  return { count : total };
}

result = db.runCommand({
  "mapreduce" : "cards",
  "map" : map,
  "reduce" : reduce,
  "out" : "suit_count"
});