NSMutableArray is not replaced object?

Question

I want to replace an array object in NSMutableArray obect. I am getting oldArray from _alertsArray and changing its value and want to replace oldArray with newArray . but there is no effect!!

NSArray *oldArray = (NSArray *)[_alertsArray objectAtIndex:[indexPath row]];
NSMutableArray *newArray = [[NSMutableArray alloc] initWithArray:oldArray copyItems:YES];
[newArray replaceObjectAtIndex:3 withObject:@"YES"];
[_alertsArray replaceObjectAtIndex:[indexPath row] withObject:newArray];

Answer 1

NSMutableArray *newArray = [_alertsArray mutableCopy];
[newArray replaceObjectAtIndex:3 withObject:@"YES"];
_alertsArray = newArray;