Loop through NSMutableArray of custom objects in the most memory efficient way

Question

What is the most memory efficient way to loop through an NSMutableArray of custom objects? I need to check a value in each object in the array and return how many of that type of object is in the array.

Answer 1

for (WhateverYourClassNameIs *whateverNameYouWant in yourArrayName) {
    [whateverNameYouWant performSelector];
    more code here;
}

It's called fast enumeration and was a new feature with Objective C 2.0, which is available on the iPhone.

Answer 2

I'd probably just use a predicate, which would be something like this:

NSArray * filtered = [myArray filteredArrayUsingPredicate:[NSPredicate predicateWithFormat:@"aProperty = %@", @"someValue"]];
NSLog(@"number of items where aProperty = someValue: %d", [filtered count]);

Edit: This code is functionally equivalent to:

NSMutableArray * filtered = [NSMutableArray array];
for (MyCustomObject * object in myArray) {
  if ([[object aProperty] isEqual:@"someValue"]) {
    [filtered addObject:object];
  }
}