Sort NSArray for a specific order - iphone

Question

I have an NSArray of custom objects.
Each object contains one integer value for ex. 1,2,3,4
Now I want to sort Array like below
9 7 5 3 1 2 4 6 8
Could some one help me?

Answer 1

Here is your answer.
Hope your first array is in sorted order (ascending) if not then you need to sort it first.
NSMutableArray *myArray = [NSMutableArray array];
//Populate your array with custom objects. I had created my own which contain an integer type property.
[myArray addObject:[[myObject alloc] initWithId:11 objectName:#"K"]];
[myArray addObject:[[myObject alloc] initWithId:3 objectName:#"C"]];
[myArray addObject:[[myObject alloc] initWithId:4 objectName:#"D"]];
....
...
.... and so on
then sort it in Ascending order. You can do it Descending also but then you need to change the below logic little bit. I showing with Ascending order.
NSArray *tempArray = [myArray sortedArrayUsingComparator:^NSComparisonResult(myObject *obj1, myObject *obj2) {
if([obj1 objectId] > [obj2 objectId]) return NSOrderedDescending;
else if([obj1 objectId] < [obj2 objectId]) return NSOrderedAscending;
else return NSOrderedSame;
}];
Now sort them as per your requirement
NSMutableArray *finalArray = [NSMutableArray arrayWithArray:tempArray];
NSInteger totalObjects = [tempArray count];
NSInteger centerObjectIndex = totalObjects>>1;
__block NSInteger rightPosition = centerObjectIndex + 1;
__block NSInteger leftPosition = centerObjectIndex - 1;
__block BOOL toggle = NO;
[tempArray enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
if(idx == 0) [finalArray replaceObjectAtIndex:centerObjectIndex withObject:obj];
else
{
if(toggle)
{
if(leftPosition >= 0)
{
[finalArray replaceObjectAtIndex:leftPosition withObject:obj];
leftPosition -= 1;
}
}
else
{
if(rightPosition < totalObjects)
{
[finalArray replaceObjectAtIndex:rightPosition withObject:obj];
rightPosition += 1;
}
}
toggle = !toggle;
}
}];
Here is the final step if your array contains an even numbers of objects
if(!(totalObjects % 2))
{
[finalArray removeObjectAtIndex:0];
[finalArray addObject:[tempArray objectAtIndex:totalObjects-1]];
}
Now you are at end. Your array named finalArray get sorted as per your requirement.