Aggregation and Restructuring data (from “R in Action”) by Dr. Robert I. Kabacoff.
From the post:
R provides a number of powerful methods for aggregating and reshaping data. When you aggregate data, you replace groups of observations with summary statistics based on those observations. When you reshape data, you alter the structure (rows and columns) determining how the data is organized. This article describes a variety of methods for accomplishing these tasks.
We’ll use the mtcars data frame that’s included with the base installation of R. This dataset, extracted from Motor Trend magazine (1974), describes the design and performance characteristics (number of cylinders, displacement, horsepower, mpg, and so on) for 34 automobiles. To learn more about the dataset, see help(mtcars).
How do you recognize what data you want to aggregate or transpose?
Or communicate that knowledge to future users?
The data set for Motor Trend magazine is an easy one.
If you have access to the electronic text for Motor Trend magazine (one or more issues) for 1974, drop me a line. I am thinking of a way to illustrate the “semantic” problem.