FAQ Series - Drilling down in Top N and Other

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 Frequently we see questions on how identify the Top N and group the "Other".

A common problem with many business applications - determining the Top N can be easily done in a number of ways.   (Presented on VizConnect - see the recording at Link to Recording)

1 The Top N filter

Just apply a Top N filter to the dimension

A more typical question adds some complexity where the user wants to see the Top N across multiple dimensions which can be solved using Index() or Rank() 

2 The Index() solution

Index is based on the position of the record in the data table so start by sorting the data:

Add the Index() (note can be hidden)

and finally add a filter set to N

It works well but there is a need to pre sort the data and when there are multiple dimensions you will need to determine which column to use in the sort: 

3 The Rank solution

An alternative is to use a ranking based on either a measure or an LOD. All forms of Rank are table calculations and look something like this:

RANK_UNIQUE(sum([Sales]),'desc')

and each segment can be treated independently without presorting the data:

4 Top N and Other

Users often want to see the Top N individually and group the remaining as "Other".  It requires a complex solution that combines both LOD's, Table Calculation, the use of Show/Hide filters and a hack 

Start with an LOD to find the Top N and "Other" based on subcategory and region (Note I am using Include to support drilling down into the Region Hierarchy) :

{ INCLUDE  [Region],[Category]:sum([Sales])}

and then Rank the LOD 

rank(sum([6 lod sales region subcat]),'desc')

to start building a data table for the viz like this 

for flexibility I added a parameter to set the N level for the Top N and created this T/F calculation

[6 rank for lod sub reg]<=[N to top N]

and used this to add a Label to the "Other" group

if [6 rank tf ] then attr([Sub-Category]) else "Other" end

 the data table now look like this:

use a table calculation to total the "Other" 

window_sum(if [6 subcat and other label]="Other" then sum([6 lod sales region subcat]) end)

and restart every Region places the Other Total on all subcategories not in the Top N - after sorting the table now looks like this

Now the hack, we only want to see each of the Top N subcategories and 1 of the subcategories labeled "Other"  in each region  - That is done with a show hide filter:

if [6 rank for lod sub reg]<=[N to top N]+1 then "show" else "hide" end

After applying the filter and hiding the real subcategory labels the data table is complete

 as a bar chart the results look like this

5 Drill down in Hierarchy

One advantage of using the Include LOD is that it supports drill into the hierarchy finding the Top N at subsequently lower levels

the LOD expression used here was 

 

{ INCLUDE  [Region],[Category]:sum([Sales])}

which will support drilling down from Region to the State level - at the Region level and filtered for Central the bar chart looks like this 

Drilling down in the Region hierarchy to the State level will return the Top N and Other unique to each state

Hope this helps the next time you need to find the Top N and group the Other

The examples used here,and a few others,  can be downloaded at workbook here

Enjoy

Jim