MongoDB中得到平均每个arrayelement
问题描述:
dbsample:MongoDB中得到平均每个arrayelement
var doc1= new BsonDocument
{
{ "line", "a" },
{ "size", new BsonArray { 2 } }
};
var doc2= new BsonDocument
{
{ "line", "xx" },
{ "size", new BsonArray { 5, 3, 8} }
};
var doc3= new BsonDocument
{
{ "line", "xx" },
{ "size", new BsonArray { 1, 10, 8} }
};
我想按行BsonDocument,得到各行的数量和每BsonArrayElement的魅力。分组和计数作品,但我怎样才能得到每个BsonArrayElement的平均值? BsonArray的长度在不同的行之间有所不同。我想
var filterBuilder = Builders<BsonDocument>.Filter;
var aggregate = collection.Aggregate().Group(new BsonDocument { { "_id", "$line" }, { "count", new BsonDocument("$sum", 1) } });
foreach (var document in aggregate.ToEnumerable())
{
Console.WriteLine(document);
}
输出:
{ "_id" : "xx", "count" : 2, "avg" : [3, 6.5, 8] }
{ "_id" : "a", "count" : 1, "avg" : [2]}
答
要获得期望的结果,你需要构建和运行聚合管道具有以下运营商:
db.collection.aggregate([
{
"$group": {
"_id": "$line",
"count": { "$sum": 1 },
"doc": { "$push": "$$ROOT" }
}
},
{ "$unwind": "$doc" },
{
"$unwind": {
"path": "$doc.size",
"includeArrayIndex": "arrayIndex"
}
},
{
"$group": {
"_id": {
"line": "$doc.line",
"idx": "$arrayIndex"
},
"avg": { "$avg": "$doc.size" },
"count": { "$first": "$count" }
}
},
{ "$sort": { "_id.idx": 1 } },
{
"$group": {
"_id": "$_id.line",
"count": { "$first": "$count" },
"avg": { "$push": "$avg" }
}
}
])
C#实现(未测试):
var result = await collection.Aggregate()
.Group(new BsonDocument {
{ "_id", "$line" },
{ "count", new BsonDocument("$sum", 1) },
{ "doc", new BsonDocument("$push", "$$ROOT") }
})
.Unwind(x => x.doc)
.Unwind(new BsonDocument {
{ "path", "$doc.size" },
{ "includeArrayIndex", "arrayIndex" }
})
.Group(new BsonDocument {
{ "_id", new BsonDocument {
{ "line", "$doc.line" },
{ "idx", "$arrayIndex" }
} },
{ "avg", new BsonDocument("$avg", "$doc.size") },
{ "count", new BsonDocument("$first", "$count") }
})
.Sort(new BsonDocument("_id.idx", 1))
.Group(new BsonDocument {
{ "_id", "$_id.line" },
{ "count", new BsonDocument("$first", "$count") },
{ "avg", new BsonDocument("$push", "$avg") },
})
.ToListAsync();
谢谢。代码在shell中工作,但在C#中我得到一个错误“'BsonDocument'不包含'doc'的定义,并且没有扩展方法'doc'接受类型'BsonDocument'的第一个参数可以被发现(你是否缺少一个使用指令或程序集引用?)“ – seeberg
正如我在答案中提到的,我没有测试过这个。当我有机会的时候,我会但是你可能需要调试管道,特别是在这个可能需要重构的'.Unwind(x => x.doc)'步骤。 – chridam
我无法得到它的工作:( – seeberg