This is the submission for the course project of Getting and Cleaning Data.
The code is in run_analysis.R. See comments inside the file.
To generate the tidy test data file, set your current working directory to the directory containing this file and then:
source("run_analysis.R")
write_X_means()
It will download and unzip the file and create a X_means_by_subject_and_activity.csv file in the current directory.