develop working R notebook to extract physical activity variables from post-processed GGIR output

[mwvoss]

Develop a starter R notebook to demonstrate how to extract physical activity variables of interest from post-processed GGIR output.

The notebook will ideally walk through

• extracting only variables needed and aggregating into a dataset that summarizes physical activity variables of interest for each subject.
• plot distributions of variables of interest to evaluate their shape and potential outliers
• guidance on how to handle outliers for any post-processing in this notebook
• save an output .csv file that the accelerometer data to be used for further analysis with other variables.