蒙戈 - 鮮明的匹配整個陣列

Question

我有一個看起來是這樣的文件：

{"arr":["a","b","c"]}, 
{"arr":["a","b","x"]}, 
{"arr":["c","b","a"]}, 
{"arr":["a","b","c"]} 

我想不過來調用不同的讓所有的獨特陣列，查詢數組默認匹配的元素，這意味着這樣的：

db.getCollection("mycoll").distinct("arr",{}); 

回報：

["a","b","c","x"] 

代替

[["a","b","c"], 
["a","b","x"], 
["c","b","a"]] 

如何查詢不同的數組？或者，我很想得到每個結果的出現次數過多：

{["a","b","c"] : 2, 
["a","b","x"] : 1, 
["c","b","a"] : 1} 

Answer 1

您可以通過arr與$sum聚集管道使用$group。

db.mycoll.aggregate({$group:{_id:"$arr", count:{$sum:1}}})