index of an of array with objects [duplicate]

Question

Input Doc:

/* 1 */
{
    "_id" : ObjectId("6237e2103cd4b19dce804712"),
    "userId" : "2701",
    "shapes" : [ 
        {
            "shape" : "square",
            "color" : "blue",
            "completed" : true
        }, 
        {
            "shape" : "circle",
            "color" : "red",
            "name" : "thisisred",
            "completed" : false
        }, 
        {
            "shape" : "rectangle",
            "color" : "red",
            "name" : "thisisred",
            "completed" : false
        }
    ]
}

How to find the indexes of Shape where color is red.

Ouput should contain:

Shapes:[1,2] // color red appears in 1st and 2nd indexed objects.

Answer 1

Use $unwind wtih includeArrayIndex

db.collection.aggregate([
  {
    $match: { "shapes.color": "red" }
  },
  {
    $unwind: {
      path: "$shapes",
      includeArrayIndex: "index"
    }
  },
  {
    $match: { "shapes.color": "red" }
  },
  {
    $group: {
      _id: "$shapes.color",
      Shapes: { $push: "$index" }
    }
  }
])

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---

Solution 2, without unwind

db.collection.aggregate([
  {
    $match: { "shapes.color": "red" }
  },
  {
    $set: {
      shapes: {
        $map: {
          input: { $range: [ 0, { $size: "$shapes" } ] },
          as: "s",
          in: {
            $mergeObjects: [
              { $arrayElemAt: [ "$shapes", "$$s" ] },
              { index: "$$s" }
            ]
          }
        }
      }
    }
  },
  {
    $set: {
      shapes: {
        $filter: {
          input: "$shapes",
          as: "s",
          cond: { $eq: [ "$$s.color", "red" ] }
        }
      }
    }
  },
  {
    $set: {
      shapes: {
        $map: {
          input: "$shapes",
          as: "s",
          in: "$$s.index"
        }
      }
    }
  }
])

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