如何在mongodb中聚合和添加值?

Question

我有以下数据集，需要按字段A分组，并将唯一值添加到现有或新字段。尝试addtoset，但没有成功。非常感谢您的帮助

数据集

A    B      C
xyz  green  blah
xyz  amber  other blah
xyz  red    asdasda
cdd  green  asdasdad 
Expected
A B
xyz,[green,amber,red]
cdd,green

.aggregate([
{"$unwind": "$RAG" }, 
{$group : {_id : {A:"$A",B:"$B"}}},testRag: { $addToSet: "$B" }]).toArray(function(err, output)

Answer 1

试试这个:

db.testCollection.aggregate([
{
$group: {
_id: "$A",
"B": {
$addToSet: "$B"
}
}
},
{
$project: {
"_id": 0,
"A": "$_id",
"B": "$B"
}
}
]);

输出:

/* 1 */
{
"A" : "cdd",
"B" : [
"green"
]
},
/* 2 */
{
"A" : "xyz",
"B" : [
"green",
"amber",
"red"
]
}