iOS: Generating random, non-repeating text

ios_random_nonrepeating_text.m

// iOS: Generating random, non-repeating text
/* 
Selects random words or phrases from an array, and only select any given word/phrase once.

To use it:
-Create a file called words.txt containing a list of words or phrases separated by carriage returns.

-Drag that file into the resources portion of your project, so it will be included in the bundle.

-Call [self buildRandomWordArray] to do the initial setup. That reads the file and populates an array of random indexes.

-Call [self getRandomWord] to get a new random word or phrase. That word/phrase will be deleted from the list and not used again. Once the list is exhausted, the getRandomWord will return nil;

-To start over and get the same list of words in a different order, call [self resetRandomArray];
_
*/

	NSArray* words;
	NSMutableArray* randomArray;
	NSMutableArray* array;
}
@property (nonatomic, retain)			NSArray* words;
@property (nonatomic, retain)			NSMutableArray* array;
@property (nonatomic, retain)			NSMutableArray* randomArray;


//This is the "sort" function that puts the items in random order.
//It uses a random number generator to decide the ordering of items in the array

NSInteger randomize(id num1, id num2, void *context)
{
	int rand = arc4random() %2;
	if (rand)
		return NSOrderedAscending;
    else 
        return NSOrderedDescending;
}

//This function populates "randomArray" with an array of indexes in random order.
//Once the getRandomWord method returns nil, call resetRandomArray to 
//repopulate the randomArray with the same list of words in a different random order.
- (void) resetRandomArray;
{
        //Copy over our starting "array" containing all our indexes in order.
	[randomArray setArray: array ];

        //Use a trick to "sort" the array into random order.
        //this trick involves using a sort function "randomize" that puts
        //the items in random order.
	[randomArray sortUsingFunction: randomize context:NULL];

}

-(NSString*) getRandomWord;
{
	if ([randomArray count] ==0)
		return nil;
	NSString* result;
	NSInteger randomIndex = [[randomArray lastObject] intValue];;
	[randomArray removeLastObject];
	result = [words objectAtIndex: randomIndex];
	return result;
}

-(void) buildRandomWordArray;
{	
	NSInteger index;
	
	NSError* theError;
	NSString *path = [[NSBundle mainBundle] pathForResource:@"words" ofType:@"txt"];
	NSString* text = [NSString stringWithContentsOfFile: path 
											   encoding: NSUTF8StringEncoding 
												  error: &theError];
	self.words = [text componentsSeparatedByString: @"\n"];
	
	int arraySize = [words count];
	self.array = [NSMutableArray arrayWithCapacity:arraySize];
	self.randomArray = [NSMutableArray arrayWithCapacity:arraySize];

        //This code fills "array" with index values from 0 to the number of elements in the "words" array.
	for (index = 0; index<arraySize; index++)
		[array addObject: [NSNumber numberWithInt: index]];
	[self resetRandomArray];
	
//	for (index = 0; index<=arraySize; index++)
//		NSLog(@"Random word: %@", [self getRandomWord]);
}