Creating unique Row IDs in Tableau Prep
Creating unique Row IDs in Tableau Prep is not something that is available out of the box, but you can use below workaround for the same effect. This is an extension to the ranking trick in Tableau Prep. Lets see how we can get unique row ids for below data.

Before going ahead, we need to make sure that there is a field that uniquely identifies each row. In our case, we can use the Name field, but if you have duplicate names, you can still get a unique field by creating a calculated field. This won’t work if you have duplicate rows and you need to perform deduping first in that case.

Now create a self inner join with criteria [Sort Key] < = Sort Key. Please note that you need a dummy step to join the data to itself.

Create an aggregation with following setting

Rename the aggregated field and add an output step, you are done.

Can be done in the first step using calc field = {ORDERBY [Sort Key] ASC: RANK()}