查询mongo以检测时间序列中的值变化 [英] Query mongo to detect value changes in time series

问题描述

我想知道在MongoDB中是否可以进行以下操作.

Im wondering if the following is possible in MongoDB.

我收集了一些表示时间上某些值发生变化的文档:

I have collection of documents that represent changes in some value in time:

{
  "day" : ISODate("2018-12-31T23:00:00.000Z"),
  "value": [some integer value]
}

数据中没有漏洞"，我有一段时间内所有天的条目.

There are no 'holes' in the data, I have entries for all days within some period.

是否可以查询此集合以仅获取具有与前一个值不同的文档(按日期升序排序时)?例如，具有以下文档:

Is it possible to query this collection to get only documents that has different value than previous one (when sorting by day asc)? For example, having following documents:

{
      "day" : ISODate("2019-04-01T00:00:00.000Z"),
      "value": 10
},
{
      "day" : ISODate("2019-04-02T00:00:00.000Z"),
      "value": 10
},
{
      "day" : ISODate("2019-04-03T00:00:00.000Z"),
      "value": 15
},
{
      "day" : ISODate("2019-04-04T00:00:00.000Z"),
      "value": 15
},
{
      "day" : ISODate("2019-04-05T00:00:00.000Z"),
      "value": 15
},
{
      "day" : ISODate("2019-04-06T00:00:00.000Z"),
      "value": 10
}

我想检索2018-04-01、2018-04-03和2018-04-06的文档.

I want to retrieve documents for 2018-04-01, 2018-04-03 and 2018-04-06.

我再次发布此问题，因为前一个被错误地标记为重复.

Im posting this question again because previous one was wrongly marked as duplicate.

推荐答案

您需要获取成对的连续文档才能检测出差距.为此，您可以将所有文档放入单个数组，然后 zip 自身从头部移了1个元素:

You need to get pairs of consecutive docs to detect the gap. For that you can push all documents into single array, and zip it with itself shifted 1 element from the head:

db.collection.aggregate([
    { $sort: { day: 1 } },
    { $group: { _id: null, docs: { $push: "$$ROOT" } } },
    { $project: {
        pair: { $zip: {
            inputs:[ { $concatArrays: [ [false], "$docs" ] }, "$docs" ]            
        } }
    } },
    { $unwind: "$pair" },
    { $project: {
        prev: { $arrayElemAt: [ "$pair", 0 ] },
        next: { $arrayElemAt: [ "$pair", 1 ] }
    } },
    { $match: {
         $expr: { $ne: ["$prev.value", "$next.value"] } 
    } },
    { $replaceRoot:{ newRoot: "$next" } }
])

其余部分很简单-您将数组展开回文档，比较对，过滤掉相等的对，然后

The rest is trivial - you unwind the array back to documents, compare the pairs, filter out the equal ones, and replaceRoot from what's left.

这篇关于查询mongo以检测时间序列中的值变化的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！