Script to Total Quantity, with Criteria, on Sales Order

@appliedtorecord

Hi. I am running the below script which is giving me the total quantity of units on my transactions. However i need to be able to only total the quantity of items that meet a certain criteria. I am using "Class" to separate my items into different categories and would need to plug in some sort of criteria into the below script. any help is appreciated.
 
/**  * Module Description  *   * Version    Date            Author           Remarks  * 1.00       08 Jul 2014     Warren  *  */   /**  * The recordType (internal id) corresponds to the "Applied To" record in your script deployment.   * @appliedtorecord recordType  *     * @param {String} type Sublist internal id  * @returns {Void}  */ function updateTotalQuantity(type, name) {   //initialize variable for total quantity   var totalQuantity = 0;      // count number of lines in 'item' sublist   var itemCount = nlapiGetLineItemCount('item');   //for each line in the 'item' sublist, add value in quantity column to the total quantity variable   for(var i=1; i<=itemCount; i++){    lineLevelQuantity = nlapiGetLineItemValue('item', 'quantity', i)    if(lineLevelQuantity != '' && lineLevelQuantity != null ) {     totalQuantity += parseInt(lineLevelQuantity);    }   }      //  assuming custbodycs_total_quantity is the custom body field for the total quantity, change its value based the value from the computation above   nlapiSetFieldValue('custbodycs_total_quantity', totalQuantity, false);  }