M101J-W5

aggregate-5.1.js

db.posts.aggregate([
	{'$unwind':'$comments'},	
	{'$match': {
		'comments.author': {
			'$ne':'machine'
		}
	}},
	{'$group': {
		'_id':'$comments.author',
		'count': {'$sum':1}
	}},	
	{'$sort': {
		'count':-1
	}},
	{'$limit':1}
])

aggregate-5.2.js

db.zips.aggregate([
	{'$match': {
		'state': {
			'$in': ['CA', 'NY']
		}
	}},
	{'$group': {
		'_id': {
			state: '$state',
			zip: '$city'
		},
		'population': {
			'$sum': '$pop' 
		}
	}},
	{'$match': {
		'population': {
			'$gt':25000
		}
	}},
	{'$group': {
		'_id': {
			state: '$state'
		},
		'population': {
			'$avg': '$population' 
		}
	}},
])

aggregate-5.3.js

db.grades.aggregate([
	{'$unwind':'$scores'},
	{'$match': {
		'scores.type': {
			'$ne': 'quiz'
		}
	}},
	{'$group': {
		'_id': {
			'class':'$class_id',
			'student':'$student_id'
		},
		'averageScore': {
			'$avg': '$scores.score'
		}
	}},
	{'$group': {
		'_id': '$_id.class',
		'classAverageScore': {
			'$avg':'$averageScore'
		}
	}},
	{'$sort': {
		'classAverageScore':-1
	}},
	{'$limit':1}
])

aggregate-5.4.js

db.zips.aggregate([
	{$project: {
		"city": {$substr : ["$city", 0, 1]},
		"population": "$pop"
     	}},	
	{"$match": {
		"city": {
			"$in": ["0", "1", "2", "3", "4", "5", "6", "7", "8", "9"]
		}
	}},
	{"$group": {
		"_id": null, 
		"total_population": {
			"$sum": "$population"
		}
	}}
]);