Question

I need to pick 32 distinctive objects from an NSMutableArray of 75 objects. it can be 1 to 32, 2 to 33 or 10 to 42. What functions should i use to get the new array? Sorry for being noob.

Answer 1

If you want N consecutive objects from a random index, try the following:

NSArray *arrayWithNConsecutiveObjects(NSArray *arr, int n)
{
    int subIdx = arc4random_uniform((unsigned) (arr.count - n));

    return [arr subarrayWithRange:NSMakeRange(subIdx, n)];
}

If you need 32 random objects, you can extend this method to randomly sort the array:

NSArray *arrayWithNObjects(NSArray *arr, int n)
{
    arr = [arr sortedArrayUsingComparator:^NSComparisonResult(id obj1, id obj2) {
        // random sort
        return arc4random_uniform(3) - 1; // one of -1, 0, and 1
    }];

    int subIdx = arc4random_uniform((unsigned) (arr.count - n));

    return [arr subarrayWithRange:NSMakeRange(subIdx, n)];
}