collection = @mongo_db.collection("identities")

    collection.mapreduce("function () {
    emit(this.d, {'identity' : this.i});
};",
                         "function(key, vals) {
  identities = [];
  for (var i=0; i<vals.length; i++) {
    identities += vals[i].identity;
  };
  return {'identity' : identities};
}};",
                         :out => "associated",
                         :verbose => true)