[{"_id":1,"stock_item":"almonds",warehouse:"B","instock":120},{"_id":2,"stock_item":"pecans",warehouse:"A","instock":80},{"_id":3,"stock_item":"almonds",warehouse:"B","instock":60},{"_id":4,"stock_item":"cookies",warehouse:"B","instock":40},{"_id":5,"stock_item":"cookies",warehouse:"A","instock":80}]

db.collection.aggregate([{$facet:{inCond:[{$group:{_id:"$stock_item",warehouses:{"$addToSet":"$warehouse"}}},{$match:{_id:"almonds"}}],docs:[]}},{"$project":{"docs":{"$filter":{"input":"$docs","as":"doc","cond":{"$in":["$$doc.warehouse",{"$arrayElemAt":["$inCond.warehouses",0]}]}}},}},{$unwind:"$docs"},{"$replaceRoot":{"newRoot":"$docs"}}])