A native list function for CouchDB that groups view results by its first key element.

group.erl

fun(Head, {Req}) ->

    Fun = fun({Row}, {PrevKey, RowCount}) ->
        Key = case couch_util:get_value(<<"key">>, Row) of
        K when is_list(K) -> hd(K);
        K -> K
        end,
        Doc = couch_util:get_value(<<"value">>, Row),
        DocJson = couch_util:to_binary(couch_util:json_encode(Doc)),
        KeyJson = <<"{\"key\":\"",Key/binary,"\"">>,
        ValueJson = <<"\"value\":[",DocJson/binary>>,
        case Key of
        PrevKey ->
            Send(<<",",DocJson/binary>>);
        _ ->
            case RowCount of
            0 ->
                Send(<<"{\"rows\":[",KeyJson/binary,",",ValueJson/binary>>);
            _ ->
                Send(<<"]},",KeyJson/binary,",",ValueJson/binary>>)
            end
        end,
        {ok, {Key, RowCount + 1}}
    end,

    FoldRows(Fun, {nil, 0}),
    Send(<<"]}]}">>)

end.