Saving fetched data on disk

I'm creating an iPhone app, which fetches information from a server ever开发者_JAVA技巧y time it is started. However, i'm planning on using the fetched data of the last month/few months/year to calculate some averages.

I had been thinking about saving them to NSUserDefaults using dictionaries (associating a date with a value), but i just remembered there also exists something like core data. Seeing that i do not have any experience with core data, i don't know if it's better. If it wouldn't, i could save the time i'd use learning it otherwise.

The data comes in in XML format, and i get several sets of the same response each time (for different locations on a map). The amount of sets can change, as the user can add more locations. I currently only save the raw data to the disk to load if the load fails next time it starts. However, i also want to save some specific values from that XML in a way that i can easily access it. What would be the best way to do this?

Edit: I actually also need to know how fast/efficient core data is. I'm currently passing around NSArrays with NSDictionaries for the sets of data during that session. For saving the data that last longer than the session core data is ideal, i found out that much (just need to find a nice way to associate an entity with a date), i just need some advice on the efficiency.

If you're going to be working with larger amounts of data, it's probably anyway better to give Core Data a try, it's after all not that complicated and there's a plenty of good tutorials where you can learn it. There are different settings for the storage type, you can either use a sqlite database or an xml file.

According to the guys from Apple, it should be fast and memory effective to use Core Data in contrast to self-made solutions, so it's a preferred way to go.

Core data would be easier to manipulate the data and query the data using predicates. Core Data supports dates so you can even find items in date ranges.