MongoDB聚合：计算数组元素或距离之间的差异
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【中文标题】MongoDB聚合：计算数组元素或距离之间的差异【英文标题】：MongoDB Aggregation: Calculate differences between array elements or distances 【发布时间】：2019-09-08 11:17:48 【问题描述】：在我的数据库中，我有一个对象在不同时间的位置。我想使用聚合来计算总行驶距离。
以下是数据示例。 “分钟”和“秒”字段提供位置的时间。 “位置”字段具有对象的 x 和 y 坐标。如何计算每两点之间的行进距离，然后求和总行进距离？
"_id" : 0,
"locations" : [
"minutes" : 43, "seconds" : 39,, "location" : [ 7.177781171570082, 8.39005423150688 ] ,
"minutes" : 43, "seconds" : 41, "location" : [ 13.239988410746804, 6.369708832879012 ] ,
"minutes" : 43, "seconds" : 51, "location" : [ 12.647876477258006, 6.288597609113424 ] ,
"minutes" : 43, "seconds" : 55, "location" : [ 12.662746868281697, 6.296370768057626 ] ,
"minutes" : 44, "seconds" : 38, "location" : [ 12.5326309468244, 6.308199488190107 ] ,
"minutes" : 44, "seconds" : 43, "location" : [ 12.53972817890389, 6.308199488190107 ] ,
"minutes" : 44, "seconds" : 53, "location" : [ 12.530265202797903, 6.310565232216604 ] ,
"minutes" : 44, "seconds" : 58, "location" : [ 12.527899458771406, 6.315296720269597 ] ,
"minutes" : 45, "seconds" : 31, "location" : [ 12.546825410983377, 6.315296720269597 ] ,
"minutes" : 45, "seconds" : 36, "location" : [ 12.542093922930384, 6.3129309762431 ] ,
"minutes" : 45, "seconds" : 45, "location" : [ 12.530265202797903, 6.3555143687200335 ] ,
"minutes" : 45, "seconds" : 40, "location" : [ 12.527899458771406, 6.341319904561056 ] ,
"minutes" : 45, "seconds" : 50, "location" : [ 12.536235756046255, 6.350367881600166 ] ,
"minutes" : 45, "seconds" : 59, "location" : [ 12.530265202797903, 6.327125440402078 ] ,
"minutes" : 45, "seconds" : 55, "location" : [ 12.546032231499275, 6.348017098292042 ] ,
"minutes" : 46, "seconds" : 14, "location" : [ 12.536573712767805, 6.3314498270318005 ] ,
"minutes" : 46, "seconds" : 18, "location" : [ 12.53972817890389, 6.3673430888525155 ] ,
"minutes" : 46, "seconds" : 23, "location" : [ 12.536525552897315, 6.364920756128036 ] ,
"minutes" : 46, "seconds" : 33, "location" : [ 11.969583868518272, 6.426486689514924 ]
]
【问题讨论】：
$range? (docs.mongodb.com/manual/reference/operator/aggregation/range) 但我不知道，你将如何转换你的：Y,X 坐标点之间的距离，
【参考方案1】：
以下查询可以得到我们预期的输出：
db.collection.aggregate([
$project:
"info":
$reduce:
"input":
$slice:["$locations",1, $size:"$locations"]
,
"initialValue":
"totalDistance":0,
"co-ordinates":
$let:
"vars":
"firstLocation":
$arrayElemAt:["$locations",0]
,
"in":
"x":
$arrayElemAt:["$$firstLocation.location",0]
,
"y":
$arrayElemAt:["$$firstLocation.location",1]
,
"in":
"totalDistance":
$sum:[
"$$value.totalDistance",
$sqrt:
$sum:[
$pow:[
$subtract:[
$arrayElemAt:["$$this.location",0]
,
"$$value.co-ordinates.x"
]
,
2
]
,
$pow:[
$subtract:[
$arrayElemAt:["$$this.location",1]
,
"$$value.co-ordinates.y"
]
,
2
]
]
]
,
"co-ordinates":
"x":
$arrayElemAt:["$$this.location",0]
,
"y":
$arrayElemAt:["$$this.location",1]
,
$project:
"_id":0,
"totalDistance":"$info.totalDistance"
]).pretty()
数据集：
"_id" : 0,
"locations" : [
"minutes" : 43,
"seconds" : 39,
"location" : [
7.177781171570082,
8.39005423150688
]
,
"minutes" : 43,
"seconds" : 41,
"location" : [
13.239988410746804,
6.369708832879012
]
,
"minutes" : 43,
"seconds" : 51,
"location" : [
12.647876477258006,
6.288597609113424
]
,
"minutes" : 43,
"seconds" : 55,
"location" : [
12.662746868281697,
6.296370768057626
]
,
"minutes" : 44,
"seconds" : 38,
"location" : [
12.5326309468244,
6.308199488190107
]
,
"minutes" : 44,
"seconds" : 43,
"location" : [
12.53972817890389,
6.308199488190107
]
,
"minutes" : 44,
"seconds" : 53,
"location" : [
12.530265202797903,
6.310565232216604
]
,
"minutes" : 44,
"seconds" : 58,
"location" : [
12.527899458771406,
6.315296720269597
]
,
"minutes" : 45,
"seconds" : 31,
"location" : [
12.546825410983377,
6.315296720269597
]
,
"minutes" : 45,
"seconds" : 36,
"location" : [
12.542093922930384,
6.3129309762431
]
,
"minutes" : 45,
"seconds" : 45,
"location" : [
12.530265202797903,
6.3555143687200335
]
,
"minutes" : 45,
"seconds" : 40,
"location" : [
12.527899458771406,
6.341319904561056
]
,
"minutes" : 45,
"seconds" : 50,
"location" : [
12.536235756046255,
6.350367881600166
]
,
"minutes" : 45,
"seconds" : 59,
"location" : [
12.530265202797903,
6.327125440402078
]
,
"minutes" : 45,
"seconds" : 55,
"location" : [
12.546032231499275,
6.348017098292042
]
,
"minutes" : 46,
"seconds" : 14,
"location" : [
12.536573712767805,
6.3314498270318005
]
,
"minutes" : 46,
"seconds" : 18,
"location" : [
12.53972817890389,
6.3673430888525155
]
,
"minutes" : 46,
"seconds" : 23,
"location" : [
12.536525552897315,
6.364920756128036
]
,
"minutes" : 46,
"seconds" : 33,
"location" : [
11.969583868518272,
6.426486689514924
]
]
输出：
"totalDistance" : 7.931893594924767
解释：我们使用$reduce 来总结每个点之间的行进距离。两点之间的距离使用以下公式计算 公式：
_______________________
Distance: √(x2−x1)^2 + (y2−y1)^2
【讨论】：
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