Database
[{"_id":ObjectId("4e8ae86d08101908e1000001"),"food":["Apples","Banana","Grapes","Pear"]},{"_id":ObjectId("4e8ae86d08101908e1000002"),"food":["Banana","Apples","Pear","Grapes"]}]
Query
db.collection.aggregate([{"$match":{"food":{$in:["Apples","Grapes"]}}},{$unwind:{path:"$food",includeArrayIndex:"index"}},{"$match":{"food":{$in:["Apples","Grapes"]}}},{"$group":{"_id":"$_id","index":{"$push":{"$toInt":"$$ROOT.index"}}}}])