Each app workspace gets its own report usage metrics data set, it’s just that you don’t see it when you are in the portal. In order to access it (at least for now) you need to use Power BI Desktop. When you open Power BI Desktop, you need to sign-in with the appropriate login, and then choose Power BI service from Get Data menu item. You then get listed with a set of app workspaces; within each you would find a list of all the datasets that were every published to each of the workspaces. Additionally, Power BI will also give you two more datasets: Report Usage Metrics Model and Dashboard Usage Metrics Model. However, these data models will only show up if you had attempted to view usage metrics at least once on one of the reports of the app workspace.
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