Mongodb mapReduce sort

sort排序是对结果按照条件排序
数据结构如下图

查询语句：
db.posts.mapReduce(function(){
emit(this.num,this.post_text)}, 
function(key,values){return values.join("# ")}, 
{
    sort:{user_name:-1},
    query:{status:"active"},
    out:"test"
}
)

db.test.find()
结果：

查询语句：
db.posts.mapReduce(function(){
emit(this.num,this.post_text)}, 
function(key,values){return values.join("# ")}, 
{
    sort:{user_name:1},
    query:{status:"active"},
    out:"test"
}
)

db.test.find()

 数据库添加语句 

db.getCollection("posts").insert( { 
"post_text": "菜鸟教程6",
"user_name": "runoob",
status: "active",
num: 16
} );