[{date:0,darwin:[{d:["string1",1,0,0,0]},{d:["string2",1,0,0,0]},{d:["string3",1,0,0,0]}]}]

db.collection.aggregate([{"$match":{"date":0}},{"$project":{"_id":0,"date":1,"darwin":{"$map":{"input":"$darwin","as":"m","in":{"d":{"$arrayElemAt":["$$m.d",0]}}}}}}])