accessing
messagesAuthors
	| groupedTweets |
	self includes at: 'users' ifAbsent: [ ^ nil ].
	groupedTweets := self data groupedBy: [:each | each at: 'author_id' ].
	^ (self includes at: 'users') collect: [:userDict |  | user |
		user := TwitterUser new fromDictionary: userDict.
		(groupedTweets at: (user id)) do: [:tweetDict | | currentTweet | 
			currentTweet := Tweet new fromDictionary: tweetDict.
			currentTweet user: user.
			user messages add: currentTweet.
		].
		user.
	  ]