Feeding a UITableViewController calculated values

Very quick question. I need to feed a UITableViewController daily averages calculated from multiple objects with an NSNumber attribute (each object is timestamped, with 8-10 objects per day usually). Is there any straightforward way to calculate on th开发者_如何学Goe fly using my own version of lazy loading (I would average data in chronological order till I had a screenful of daily averages) or should I just take the easy way out and maintain an Averages entity pre-populated with averages for all possible days, which I present conventionally in my UITableViewController?

Thanks.

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Depends how long the calculation takes? Why not just calculate it in the UITableViewDataSource method that asks for the cellForRowAtIndexPath? Unless it takes time to calculate - thereby causing a delay in populating the values onscreen - I'd say there's no harm in calculating on the fly.

There's plenty of other places to do the calculation. You could do it on app startup, or on loading the view. You could even start an NSOperation that does it in the background with the controller as a delegate that tells it when to reloadData.

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You should do a fetch by value (see Core Data Programming Guide) and then use the @avg collections operator on the attribute name.