如何获得聚合的前 n 个存储桶,以及将所有其他存储桶组合成“其他"存储桶?桶? [英] How can I get top n buckets for an aggregation and all other buckets combined into an "other" bucket?
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问题描述
假设一个集合的模式如下所示:
Assume a collection with schema like as shown below:
{
"customer" : <unique-id-for-customer>,
"purchase" : <number>,
}
现在,我想获得前 5 位客户(按购买数量),第 6 个桶是其他",它结合了其他客户的所有购买数量.
Now, I want to get the the top 5 customers (by purchase-queantity) and the 6th bucket is "others" which combines all the purchase quantity from other customers.
基本上,聚合的输出应该是这样的:
Basically, the output of aggregation should be like:
{ "_id" : "customer100", "purchasequantity" : 4000000 }
{ "_id" : "customer5", "purchasequantity" : 81800 }
{ "_id" : "customer4", "purchasequantity" : 40900 }
{ "_id" : "customer3", "purchasequantity" : 440 }
{ "_id" : "customer1", "purchasequantity" : 300 }
{"_id" : "others", "purchasequantity" : 29999}
推荐答案
你想要的叫做 权重.为此,您需要通过 $project 为您的文档添加权重
使用它们并使用 $cond
运算符,然后按权重"升序排序,购买数量"降序排序.
What you want is called weighting. To do that you need to add a weight to your documents by $project
ing them and using the $cond
operator, then sort them by "weight" in ascending other and by "purchasequantity" in descending order.
db.collection.aggregate([
{ "$project": {
"purchasequantity": 1,
"w": {
"$cond": [ { "$eq": [ "$_id", "others" ] }, 1, 0 ]
}
}},
{ "$sort": { "w": 1, "purchasequantity": -1 } }
])
返回:
{ "_id" : "customer100", "purchasequantity" : 4000000, "w" : 0 }
{ "_id" : "customer5", "purchasequantity" : 81800, "w" : 0 }
{ "_id" : "customer4", "purchasequantity" : 40900, "w" : 0 }
{ "_id" : "customer3", "purchasequantity" : 440, "w" : 0 }
{ "_id" : "customer1", "purchasequantity" : 300, "w" : 0 }
{ "_id" : "others", "purchasequantity" : 29999, "w" : 1 }
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