根据公式计算 AVG [英] Calculate the AVG based on a formula

问题描述

我有以下输入:

{
   "_id":"series/cogtech/BertonKHS06",
   "type":"Article",
   "title":"Speech Recognition.",
   "pages":{
      "start":85,
      "end":107
   },
   "year":2006,
   "booktitle":"SmartKom",
   "url":"db/series/cogtech/54023732.html#BertonKHS06",
   "authors":[
      "Andr? Berton",
      "Alfred Kaltenmeier",
      "Udo Haiber",
      "Olaf Schreiner"
   ]
}

我想按书获得平均页码.

I want to get the average page numbers by book.

一本书有开始页和结束页.

A book has a start and an end page.

计算平均值:AVERAGE=(end - start)/2我怎样才能做到这一点?

To calculate the average : AVERAGE=(end - start)/2 How can I achieve this ?

推荐答案

• $subtract 为减法，$divide 为除法，
• $subtract for minus and $divide for devide,

db.collection.aggregate([
  {
    $addFields: {
      average_pages: {
        $divide: [
          { $subtract: ["$pages.end", "$pages.start"] },
          2
        ]
      }
    }
  }
])

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