Limit number of data points on graph

[#1]

I have a graph (Store Type vs. Num of Customer visits) where I load all of my data from database and I have many filters(Customer, Date, membership status, Store, etc..) for that data. I want to be able to show only the latest 20 visits from a customer after all my filters are applied. So for example I would want to have the last 20 visits when I select a certain customer visiting a certain store, or the last 20 visits when I select all customers with a certain membership status visiting a certain store. Is there any way I can so this?

Thanks

[Anil_Babu_Samineni]

Can we know which chart you are using? May be dimension limits tab on Object properties and give Last 20 values. Meantime, The tab is not available may be look Rank() function

[#3]

I am using a bar chart, problem with dimension limits is that I am not limiting the last 20 values of the dimension, but overall datapoints on the graph, which is shown by my expression, how can I use rank?

[Anil_Babu_Samineni]

May be this?

Aggr(If(Rank(Sum(Sales))<=20, Sum(Sales),Dim1)