How to get distinct pages visited per user

[jamesleslie]

I have a table containing user activity logs for a website.
Each row in the table represents a user visiting a specific page on the website.

I would like to make a new table using DAX to get total (distinct) pages visited per user.
The table below is an example of my activity table: 

UserId	PageId
A	1
A	2
B	1
C	2
C	1
C	2

I would like to get a table that looks like this (C appears 3 times above, but only visited 2 distinct pages):

UserId	NumPages
A	2
B	1
C	2

I can achieve this in Power Query by using GroupBy twice in a row, but this feels hacky.

[amitchandak]

You can use

measure = distinctcount(Table[pageID])

In case you want GT to be the sum of lines

sumx(values(table[UserID]),[Measure])
sumx(summarize(table,table[UserID],"_dist",[Measure]),[_dist])