Let's be fair, in Objective-C, this could be actually more like

  NSIndexSet *indicies = [allRecords indexesOfObjectsPassingTest:^ (id obj, NSUInteger idx, BOOL *stop) { return [obj someField] == someFieldFilterValue; }];
  filteredArray = [allRecords objectsAtIndexes:indicies];

rather than what the article had in mind.

EDIT: oh, someFieldFilterValue was an integer, wasn't it. Fixed.