Performing fast aggregation with a data.table

Another advantage of a data.table is that we can easily aggregate data without the help of additional packages. In this recipe, we will illustrate how to perform data aggregation using data.table.

Getting ready

Ensure that you completed the Enhancing a data.frame with a data.table recipe to load purchase_view.tab and purchase_order.tab as both a data.frame and a data.table into your R environment.

How to do it…

Perform the following steps to perform data aggregation over data.table:

1. First, we can average the price of orders in total:

   > order.dt[,mean(na.omit(Price))]
   [1] 2012.119
   

2. Next, we can average the amount of orders per user:

   > mean.price.by.user <- order.dt[,mean(na.omit(Price)), User]
   > head(mean.price.by.user)
              User      V1
   1:   U312622727  934.00
   2:   U239012343 1298.75
   3: U10007697373  247.00
   4:   U296328517  745.00
   5:   U300884570  249.00
   6:   U451050374 1780.00
   

3. In order to name the aggregated data, we can surround...