Class 13: Collecting Tidy Data
We are going to start today by having you all open either excel, open office, Google sheets, or the spreadsheet editor of your choice.
You will be constructing a dataset representing a set of ten films of your choosing.
Please collect the following (I suggest starting with Wikipedia and going to IMDb and rotten tomatoes for the rest):
- name of the movie
- movie budget
- country of origin
- date first released
- staring actors (truncate to top 3 if too many)
- birthplace of each actor
- rotten tomatoes rating of the movie
If you have time remaining before we come back together as a group, try to download the file and read it into R.
All of the principles of constructing a dataset (equivalently, a database) could easily fill a whole course. Here are three principles that get us on the right track:
- determine the objects of study; each of these gets its own table, and each example gets its own row; movies, actors, actor-movie links
- each column should be indivisible and the variable type clear; for example, budget should not include the dollar sign, if needed create a new column; name columns with no spaces or special characters
- always have internal consistency (0.62 or 62 percent; missing values always “NA”); strive for external consistency (ISO country codes)
If you would like to know about specifics of these principals I highly recommend the Hadley Wickhams “Tidy Data” paper:
The Tidy Data chapter of R for Data Science covers several useful functions the show to convert a dataset that has already been collected into a tidy format:
While I love the principles of Tidy Data, and find great value in the dplyr and ggplot2 packages, I personally do not think the tidyr package (documented in the R4DS chapter) are particularly helpful. Eventually you’ll find something that needs to be handled outside of those specific tools so it is just better to learn how to clean data using base-R or stringi functions.
In our next class we will see how to link together the multiple tables that we have just built.