Create a Distinct Count Column that can be summed to get a Distinct Count Total

Hello - I am trying to create a new column that will contain a fraction that when summed, it will equal the total number of distinct counts for a column.  In the Example Below, the Value I am trying to create would be .33333 because there are 3 ABC's and when summed it would equal 1 (1 distinct count).  ABD would be .5 since there are 2 ABDs.  If there were 4 values it would be .25, etc.