console session

(vagrant@127.0.0.1)1> {ok, Client} = riak:client_connect('riak@10.0.2.15').
{ok,{riak_client,'riak@10.0.2.15',<<3,172,224,28>>}}
(vagrant@127.0.0.1)2> {ok, [R]} = Client:mapred([{<<"groceries">>, <<"mine">>},
(vagrant@127.0.0.1)2>                              {<<"groceries">>, <<"yours">>}],
(vagrant@127.0.0.1)2>                             [{'map', {modfun, triggers, count}, 'none', false},
(vagrant@127.0.0.1)2>                              {'reduce', {modfun, triggers, merge}, 'none', true}]).
** exception error: no match of right hand side value {error,{error,undef,
                                                                    [{triggers,count,
                                                                               [{r_object,<<"groceries">>,<<"mine">>,
                                                                                          [{r_content,{dict,2,16,16,8,80,48,
                                                                                                            {[],[],[],[],...},
                                                                                                            {{[],[],...}}},
                                                                                                      ["eggs","bacons"]}],
                                                                                          [{<<7,251,249,244>>,{1,63479791411}}],
                                                                                          {dict,1,16,16,8,80,48,{[],[],[],[],[],...},{{[],[],[],...}}},
                                                                                          undefined},
                                                                                undefined,none]},
                                                                     {riak_kv_mapper,run_map,9},
                                                                     {riak_kv_mapper,'-do_map/2-fun-0-',9},
                                                                     {lists,foldl,3},
                                                                     {riak_kv_mapper,do_map,2},
                                                                     {gen_fsm,handle_msg,7},
                                                                     {proc_lib,init_p_do_apply,3}]}}

triggers.erl

-module(triggers).
-export([count/3, merge/2]).

count(G, _, _) ->
    [dict:from_list([{I, 1} || I <- riak_object:get_value(G)])].

merge(Gcounts, _) ->
    [lists:foldl(fun(G, Acc) ->
                            dict:merge(fun(_, X, Y) -> X+Y end,
                                       G, Acc)
                          end,
                          dict:new(),
                          Gcounts)].