R for Data Science Cookbook

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) ...