Arrays Mongodb基于另一个数组元素筛选数组
假设我有如下文档Arrays Mongodb基于另一个数组元素筛选数组,arrays,mongodb,mongodb-query,Arrays,Mongodb,Mongodb Query,假设我有如下文档 { "_id" : 1, "Quality" : [ "HIGH", "LOW", "LOW", "HIGH" ], "Pages" : [ 10, 10, 12, 17 ] } 我需要结果 { "_id" : 1, "HIGH" : 27 "LOW" : 22 } 我需要通过求和Pages数组中相应的索引位
{
"_id" : 1,
"Quality" : [
"HIGH",
"LOW",
"LOW",
"HIGH"
],
"Pages" : [
10,
10,
12,
17
]
}
我需要结果
{
"_id" : 1,
"HIGH" : 27
"LOW" : 22
}
我需要通过求和Pages数组中相应的索引位置值,根据质量创建两个属性HIGH和LOW
我曾想过使用$filter和$arrayElemAt,但在页面属性上进行筛选时无法获得索引位置
high : { $sum:{ $filter: { input: "$Pages", as: "noOfPages", cond: {"$eq":[{ $arrayElemAt: ["$Quality", **Need to pass index position of $pages while filtering**]}, "HIGH"]}}}}
提前感谢。您可以使用下面的聚合
db.collection.aggregate([
{ "$project": {
"Quality": {
"$map": {
"input": { "$range": [0, { "$size": "$Quality" }] },
"in": {
"Quality": { "$arrayElemAt": ["$Quality", "$$this"] },
"Pages": { "$arrayElemAt": ["$Pages", "$$this"] }
}
}
}
}},
{ "$project": {
"newArrayField": {
"$map": {
"input": { "$setUnion": ["$Quality.Quality"] },
"as": "m",
"in": {
"k": "$$m",
"v": {
"$filter": {
"input": "$Quality",
"as": "d",
"cond": {
"$eq": ["$$d.Quality", "$$m"]
}
}
}
}
}
}
}},
{ "$project": {
"d": {
"$arrayToObject": {
"$map": {
"input": "$newArrayField",
"in": {
"k": "$$this.k",
"v": { "$sum": "$$this.v.Pages" }
}
}
}
}
}}
])
可以通过两个聚合阶段实现这一点 首先是将两个数组映射到单个数组中 第二种方法是过滤单个数组,使其仅包含高(/LOW),并将过滤后的数组减少为单个和元素
[{$project: {
"Quality": {
$map: {
input: {$range: [0, {$size: "$Quality"}]},
as: "idx",
in: {
"Quality": { $arrayElemAt: ["$Quality", "$$idx"] },
"Pages": { $arrayElemAt: ["$Pages", "$$idx"] }
}
}
}
}}, {$project: {
"HIGH": {
$reduce: {
input: {
$filter: {
input: "$Quality",
as: "x",
cond: {$eq: ["$$x.Quality", "HIGH"]}
}
},
initialValue: 0,
in: {
$add: ["$$value", "$$this.Pages"]
}
}
},
"LOW": {
$reduce: {
input: {
$filter: {
input: "$Quality",
as: "x",
cond: {$eq: ["$$x.Quality", "LOW"]}
}
},
initialValue: 0,
in: {
$add: ["$$value", "$$this.Pages"]
}
}
}
}}]
这正好满足了您的要求:
{
_id: 1
HIGH:27
LOW:22
}
我甚至可以用一个聚合阶段来实现这一点,但为了更好地阅读,我更喜欢多个阶段。您的答案的问题是,您已经将“高”和“低”硬编码。有没有一种方法可以将$subtract与$$this结合使用,例如从数组中获取上一项?