I need to calculate the percentile distribution for an aggregated data set that finds the 15th percentile of all dates prior that day. For example, in the table below, each product/type would have a 15th% value for date 1/12/2025 that uses all dates prior (1/11/2025,1/10/2025). Each day would bring another day into the percentile dataset. 1/13/2025 would calculate a 15th percentile using 1/10,1/11,1/12.
I've been working with fractile combined with above and aggr but cannot seem to get it to work
