In this final subsection, we will show how to perform another very common operation quickly and efficiently in data.table. This operation has many names—pivot-table-ing, reshaping, melting/casting, spreading/gathering, converting from long to wide (or vice-versa). But while the nomenclature, I admit, can get pretty complicated, understanding the concept doesn’t have to be! The best first step to explaining this is by the following example:
Here is an example of data that we will, heretofore, refer to as in long format:
year themonth N 1: 2016 Sep 225 2: 2016 Aug 215 3: 2016 Jul 411 4: 2016 Jun 169 5: 2016 May 478 --- 103: 2008 Feb 984104: 2008 Jan 877105: 2016 Mar 360106: 2016 Oct 258107: 2016 Nov 124 ...
