[{"_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}]}]

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