MongoDB MapReduce 分组统计

var map=function(){
emit(this.description,{"count":1});
}

var reduce=function(key,values){

var total=0;

for(var i=0; i < values.length; i++){

total+=values[i].count;

}

return {count:total}
}

db.runCommand({"mapreduce":"statistics_securitylog","map":map,"reduce":reduce,"out":"test.tmp"});

/* 0 */
{
"_id" : "用户登录",
"value" : {
"count" : 2608.0
}
}

/* 1 */
{
"_id" : "用户退出",
"value" : {
"count" : 396.0
}
}