This content has 13 years. Please, read this page keeping its age in your mind.
When you cope with data is better to visualize it.
A nice framework for iPhone is Core Plot, has many capabilities and is bast at the moment. The last version is 0.9
The only serious problem I faced, is the lack of documentation for the first steps. Specifically if you are using Xcode 4.2… the situation is getting harder.
I found only one tutorial that uses the last Xcode. You can find it in Dr John Wordsworth site and specifically here.
Enjoy!