Databases
Start Lecture 6 at page 5 with how a variable’s meaning determines useful comparisons. Practice data types in Classwork 8, then learn how databases, tables, and keys support left_join() in Classwork 9.
Start Lecture 6 at page 5, A variable’s meaning determines useful comparisons. Complete Classwork 8: Taxonomy of Data, then continue into databases, tables, and keys and practice left_join() in Classwork 9: Combining Tables with left_join().
The midterm is October 19.
Use the Midterm Exam Guide to review the planned coverage and practice multiple-choice, fill-in-the-blank, and short-answer questions.
Tentative midterm coverage: Lectures 1–6. Check Brightspace for final instructions.
Focus
- What different measurement scales let us compare
- Relational tables and key variables
- Matching tables with left_join()
Prepare
- Start Lecture 6 at page 5
- Have Classworks 8 and 9 ready in Posit Cloud
- Identify what a row represents in each table
Practice
- Classify variables in Classwork 8
- Match students to their majors in Classwork 9
- Explain retained rows, unmatched keys, and missing values
Learning targets
- Distinguish nominal, ordinal, interval, and ratio variables using their meaning and context.
- Explain what each row represents in a relational table.
- Identify the key variable used to match records between tables.
- Explain which rows
left_join()retains and how unmatched rows appear in the result. - Connect data types, databases, and keys to an analytical question.
- Check for unmatched keys and repeated reference keys before relying on a join result.
Check the table match
Before left_join(), identify what each row represents, the key variable used to match the tables, and whether the right table has one record per key. After the join, check that all left-table rows are retained and that unmatched rows have NA for columns from the right table.
Lecture slides
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