/* Main rule in your a!gridField() */
a!gridTextColumn(
  label: "Product",
  field: "PRODUCT_CATEGORY",
  data: apply(
    rule!productCatOrDesc(
      productCategory: local!productCategory,
      productCategoryArray: index(
        local!products.data,
        "PRODUCT_CATEGORY",
        {}
      ),
      productDescription: local!productDescription,
      productDescriptionArray: index(
        local!products.data,
        "PRODUCT_DESCRIPTION",
        {}
      ),
      idx: _
    ),
    1 + enumerate(
      count(
        local!products.data
      )
    )
  )
)

/* Sub Rule Definition */
productCatOrDesc(	productCategory Number, 
					productCategoryArray Number (Multiple),
					productDescription Number,
					productDescriptionArray Number (Multiple),
					idx Number
				)
/* Sub Rule */
with(
  local!data: if(
    rule!APN_isBlank( /* assumes you have Appian common objects */
      ri!productDescritpionArray[ri!idx]
    ),
    rule!RADARR_ER_applyCategoryByCategoryID(
      productCategory: ri!productCategory,
      categoryID: ri!productCategoryArray[ri!idx]
    ),
    rule!RADARR_ER_applyDescriptionNameByDescriptionID(
      productDescription: ri!productDescription,
      descriptionID: ri!productDescriptionArray[ri!idx]
    )
  )
)