Worst 15 Products in Calculated Dimension

[Fq]

Hi, I am using the following expression to calculate the Growth Rate of the Products in the last 60 days (Rolling).

(
Sum({<Date = {"$(='>=' & Date(Today() - 60, 'YYYY-MM-DD'))"}>} Sum(Units))
-
Sum({<Date = {"$(='>=' & Date(Today() - 120, 'YYYY-MM-DD') & '<=' & Date(Today() - 61, 'YYYY-MM-DD'))"}>} Sum(Units))
)
/
Sum({<Date = {"$(='>=' & Date(Today() - 120, 'YYYY-MM-DD') & '<=' & Date(Today() - 61, 'YYYY-MM-DD'))"}>} Sum(Units))

The thing is I need to create a calculated dimension with the worst 15 Products in terms of Growth Rate.

Why? Because I have more than 50,000 Products and I want to display in a Chart only a 15 of them, and the user with a button will be able to select top 15 or bottom 15. 

For Top 15 Products I created the following expression, which is working perfect:

Aggr(
if(rank((
Sum({<Date = {"$(='>=' & Date(Today() - 60, 'YYYY-MM-DD'))"}>} $(vUnits))
-
Sum({<Date = {"$(='>=' & Date(Today() - 120, 'YYYY-MM-DD') & '<=' & Date(Today() - 61, 'YYYY-MM-DD'))"}>} $(vUnits))
)
/
Sum({<Date = {"$(='>=' & Date(Today() - 120, 'YYYY-MM-DD') & '<=' & Date(Today() - 61, 'YYYY-MM-DD'))"}>} $(vUnits))
) <= 15, [Product Name]),
[Product Name]
)

However I am struggling a lot to create a calculated dimension for the bottom 15 Products. 

[MartW]

what kind of visualisation are you using?

if you are using a bar chart.

isn't it easier to just select the top/ or bottom x products (productname a dimension) and a simple $(vUnits) as a messure. maybe with some extra set analysis to filter on last 60 or last 30 days.

[Fq]

Unfortunately it is not possible, because the idea is a toggle where you can select the Top 15 based on Growth, based on Sales, based on YoY%, Worst Products based on Growth, Worst Products based on Sales, etc. 

But the measure of the bar chart will be always the same, so that measure will apply to the top 15 based on the filter selected. And for some reason the bar chart doesn't let you change the expression you want to use to select the top N, it automatically use the one of the bar chart.