Julia Programming Projects

@where

One of the most useful commands is @where, which allows us to filter a data source so that only the elements that satisfy the condition are returned. Similar to @select, the condition can be any arbitrary Julia expression:

julia> @from p in shopping_list begin 
           @where p.qty < 2 
           @select p 
           @collect DataFrame 
       end 

We get the following output:

Only bread has a qty smaller than 2.

Filtering can be made even more powerful by means of range variables. These act like new variables belonging to the query expression and can be introduced using the @let macro:

julia> @from p in shopping_list begin @let weekly_qty = 7p.qty @where weekly_qty > 10 ...