How to perform this mongo aggregation?

Question

I have a collection in mongo that looks like this:

{
    "_id" : ObjectId("5c98d6f383d67f243730443b"),
    "date" : ISODate("2019-03-24T00:00:00Z"),
    "symbol" : "F:ABCD",
    "symbolCode" : "wcgahi8gap",
    "close" : 8.09,
    "high" : 24.82,
    "low" : 8.09,
    "numPoints" : 8,
    "open" : 20.84,
    "volume" : 21183
}
{
    "_id" : ObjectId("5c98d6f383d67f243730443c"),
    "date" : ISODate("2019-03-25T00:00:00Z"),
    "symbol" : "F:ABCD",
    "symbolCode" : "wcgahi8gap",
    "close" : 1.77,
    "high" : 23.47,
    "low" : 1.77,
    "numPoints" : 3,
    "open" : 8.21,
    "volume" : 9645
}

Which shows the prices of stocks at end of day. I'm trying to write an aggregation to calculate the change/percent change for each stock in the 1 day interval. So it should just be the difference between the current days close field and the previous day close field. How can I do this?

This is what I have so far:

  const results = await Price.aggregate([
    { $match: { date: { $gte: yesterday } } },
    { $sort: { date: 1 } },
    { $group: { '_id': '$_id',
      'old': {
        $sum: { $cond: [{ '$eq': [ '$date', yesterday ] }, '$close', 0] }
      },
      'new': {
        $sum: { $cond: [{ '$eq': [ '$date', today ] }, '$close', 0] }
      } } },
    { $project: { date: 1, symbol: 1, difference: { $subtract: ['$new', '$old'] } } }
  ])

I know I'm missing an important part of the group stage but I can't figure it out.

score 0 · Answer 1 · answered Mar 25 '19 at 14:59

So here's how I did it:

  const results = await Price.aggregate([
    { $match: { date: { $gte: yesterday } } },
    { $sort: { date: 1 } },
    { $group: { '_id': '$symbol',
      old: {
        $sum: {
          $cond: [{ $eq: ['$date', yesterday] }, '$close', 0]
        }
      },
      new: {
        $sum: {
          $cond: [{ $eq: ['$date', today] }, '$close', 0]
        }
      } } },
    { $project: {
      symbol: '$_id',
      change: { $subtract: ['$new', '$old'] },
      changePrc: { $divide: [{ $subtract: ['$new', '$old'] }, '$old'] }
    } }
  ])

Used this answer for help.

How to perform this mongo aggregation?

1 Answers1