gistfile1.m

if(stocks)
    {
        NSMutableDictionary *serialStocks = [NSMutableDictionary dictionary];
        
        for (NSString *key in stocks) {
         
            NSMutableArray *serialPurchases = [NSMutableArray array];
            
            NSArray *item = [stocks objectForKey:key];
            if ([item isKindOfClass:[NSArray class]]) {
                
                for (StockPurchase *purchase in item) {
                    
                    NSDictionary *serialPurchase = [purchase serializeToDictionary];
                    [serialPurchases addObject:serialPurchase];
                    
                }//purchase in item
                
                
            }//if array
            
            [serialStocks setObject:serialPurchases forKey:key];
            
        }//ket in stocks
    }