you can use findPageList api based on entered ID, it will return ArrayList of same IDs, then convert the ArrayList to ClipboardProperty then use countInPageList on ClipboardProperty based on measures , if count >1 then duplicate measures entered for that id.

Ex:

ID1 Mesure1

ID2 measure2

ID1 Measure3        Assure after third row user added below row i.e ID1 Measure1

ID1 Measure1

Now use my above explanation ....

first send the list to findPageList  by ID1, it will return arrayList with three items like below

 ID1 Mesure1,  ID1 Measure3,  ID1 Measure1

first and third have the same measure. we need to find it by using the countInPageList api

Now use the countInPageList based on measure property. Measure1 is repeated two times and count returns 2. which is >1, then you can say its duplicate mesure for same id.

let me know if you have any questions.

param.DuplicateCheckResult  =@CheckDuplicatesInPageList((Primary.DetailsPage.CountryList),".CountryCode",tools,@Utilities.getLocalizedText("CantHaveSameCountryTwice",pyMessageLabel,tools),true)

Try this above function, This function will tell you whether there any duplicate entries or not based on

.CountryCode  <--- Key property

.CountryList   <-- Pagelist property

CantHaveSameCountryTwice <-- Field value for display message