Aggregation framework

In this type of queries the results of several partial queries are merged and grouped together to form a new result. The following query returns a list of all US states, that have more than 10 million inhabitants.

[
	{ 
		$group : { 
			_id : "$state",
            totalPop : { 
				$sum : "$pop"
			} 
		} 
	},
	{ 
		$match : { 
			totalPop : {
				$gte : 10000000
			} 
		}
	}
]

The queries must be embedded in an array. Are the appropriate braces left out, it leads to an error message.

A detailed documentation of the MongoDB AggregationFramework can be found here: http://docs.mongodb.org/manual/core/aggregation-introduction/