sample_reduce.js

{
	{
		"username": "bobo",
		"emails": [ "foo@bar.com", "foo@baz.com" ]
	}
  {
		"username": "theclown",
		"emails": [ "baa@bar.com", "fooor@baz.com" ]
	}
}

"email_appears": {
	"map": "function(doc) { 
		for (x in doc.emails) { 
			emit(x, doc.username);
		}
	}",
	"reduce": "function(keys, values) {
		return values.count;
	}"
}