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Answer 1

+2 A:

Generate a random number and use it as the index.

Graham Lee 2010-07-23 14:11:43

So simple and yet it works so well!

Joshua 2010-07-23 14:20:09

@Joshua if you want a little more detail, you can use `SecRandomCopyBytes()` to get cryptographically-useful random numbers, on the iPhone anyway. On Mac you have direct access to /dev/random.

Graham Lee 2010-07-23 14:31:32

@Graham A Random Number should suffice but thanks anyway for the added information.

Joshua 2010-07-23 14:37:50

Answer 2

+2 A:

Perhaps something along the lines of:

NSUInteger randomIndex = (NSUInteger)floor(random()/RAND_MAX * [theArray count]);

Don't forget to initialize the random number generator (srandomdev(), for example).

NOTE: I've updated to use -count instead of dot syntax, per the answer below.

Darryl H. Thomas 2010-07-23 14:19:52

That's even better, thanks for including a code snippet!

Joshua 2010-07-23 14:30:28

Answer 3

+3 A:

@Darryl's answer is correct, but could use some minor tweaks:

NSUInteger randomIndex = arc4random() % [theArray count];

Modifications:

Using arc4random() over rand() and random() is simpler because it does not require seeding (calling srand() or srandom()).
The modulo operator (%) makes the overall statement shorter, while also making it semantically clearer.
theArray.count is wrong. It will work, but count is not declared as an @property on NSArray, and should therefore not be invoked via dot syntax. That it works is simply a side-effect of how dot syntax is interpreted by the compiler.

Dave DeLong 2010-07-23 14:39:38

Note that RC4/ARC4 doesn't give uniform output.

Graham Lee 2010-07-23 15:01:20

Thanks for your suggestions.

Darryl H. Thomas 2010-07-23 15:22:26

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Picking a Random Object in an NSArray.

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