stock category help needed !!!

Dear Admin & Experts,

Can you tell me how to extract stock category using below collection


[Collection: CFBK Summ Voucher]
Source Collection: CFBK Voucher
Walk: Inventory Entries
By: PName: $$Monthstart:$Date
By: IName: $partyledgername
By: StName: $stockcategory ****************** this is not working
By: uIName: $$unitsymbol:$billedqty
Aggr Compute: BilledQty: SUM: $BilledQty
Aggr Compute: Billeamtt: SUM: $Amount
compute: stnamec: $OnlyAlias:StockItem:$StockItemName
Search Key: $PName + $IName + $stname + $uiname


Thanks
Johar