蒙戈 - 鲜明的匹配整个阵列

Question

我有一个看起来是这样的文件：

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

我想不过来调用不同的让所有的独特阵列，查询数组默认匹配的元素，这意味着这样的：

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

回报：

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

代替

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

如何查询不同的数组？或者，我很想得到每个结果的出现次数过多：

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

Answer 1

您可以通过arr与$sum聚集管道使用$group。

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