``` library(data.table) purchases[amount <= median(amount)*10][, .(total = sum(amount - discount)), by = .(country)][order(country)] ``` - no quotes needed -

``` library(data.table) purchases[amount <= median(amount)*10][, .(total = sum(amount - discount)), by = .(country)][order(country)] ``` - no quotes needed - no loc needed - only 1 groupby needed