Filter specific nodes based on value in XSLT

Question

I have the following variable which I use to calculate a sum of revenue for a customer.

                    <xsl:variable name="revenue">
                        <xsl:value-of select="format-number(sum(//fn:array[@key= 'Items']/fn:map/fn:map[@key ='Amount']/*[@key = 'Net']),'##.##')" />
                    </xsl:variable>    

I would like to filter based on Type, as you can see from the JSON object below:

 "Items":[
            {
               "Id":"5eab80a9-7d1c-4dc3-a6df-aca4015519b2",
               "CustomerId":"0db08884-3218-4c38-b895-aca4014fa598",
               "OrderId":"7965b5fc-fb21-472e-a862-aca401551900",
               "ServiceId":"bd26d8db-86da-4f96-9efc-e5a4654a4a94",
               "ProductId":null,
               "BillId":"2f5009f7-b1d8-4138-a2ac-aca60099a6ca",
               "InvoiceId":null,
               "AccountingCategoryId":"0cf7aa90-736f-43e9-a7dc-787704548d86",
               "CreditCardId":null,
               "Type":"ServiceRevenue",
               "SubType":"SpaceOrder",
               "Name":"Night 02/01/2021",
               "Notes":null,
               "ConsumptionUtc":"2021-01-02T14:00:00Z",
               "ClosedUtc":"2021-01-04T09:19:46Z",
               "State":"Closed",
               "SubState":null,
               "Amount":{
                  "Value":100.00,
                  "Net":95.24,
                  "Tax":4.76,
                  "TaxRate":0.05,
                  "Currency":"GBP",
                  "NetValue":95.24,
                  "GrossValue":100.00,
                  "TaxValues":[
                     {
                        "Code":"UK-2020-R",
                        "Value":4.76
                     }
                  ]
               }
            },

I tried the following but does't work:

 <xsl:value-of select="format-number(sum(//fn:array[@key= 'Items']/fn:map/fn:map[@key ='ServiceType']='ServiceRevenue'/fn:map[@key ='Amount']/*[@key = 'Net']),'##.##')" />

Answer 1

I think you want e.g.

                    <xsl:value-of select="format-number(sum(//fn:array[@key= 'Items']/fn:map[fn:string[@key = 'ServiceType'] = 'ServiceRevenue']/fn:map[@key ='Amount']/*[@key = 'Net']),'##.##')" />