Multiple Choices: Joining Data Frames

1. Which of the following dplyr functions keeps only the rows that have matching values in both tables?

left_join() right_join() inner_join full_join

2. What does left_join return when used on two data frames?

All rows from the right table and only matching rows from the left table. Only the rows with matching values in both tables. All rows from the left table and matching rows from the right table. All rows from both tables, with NA for non-matching rows.

3. Which function includes all rows from both tables, with NA values in place where there are no matches?

left_join() right_join() inner_join full_join

4. If right_join is applied to two tables, what will the result include?

Only rows with matching values in both tables. All rows from the left table and matching rows from the right table. All rows from the right table and matching rows from the left table. All rows from both tables, filling unmatched rows with NA.

5. Which of the following commands can help avoid NA values when joining data with only common records between two data frames?

left_join() right_join() inner_join full_join

6. What argument should you use in dplyr joins to specify which columns to join by, if the column names differ between two tables?

by match_columns join_columns merge

7. Which dplyr join function would be best suited for combining a table of employees with another table of department names, ensuring that every employee appears, even if they don’t have a department?

left_join() right_join() inner_join full_join

8. What is the outcome if full_join is used on two data frames with no matching keys?

A table with no rows. A table with all rows from both data frames, with NA for missing values in each. Only the rows that match in both data frames. All rows from the first data frame only.

9. When using inner_join, what happens to rows in either data frame that do not have matching keys in the other data frame?

They are included with NA values. They are excluded from the result. Only the first data frame's unmatched rows are included. Only the second data frame's unmatched rows are included.

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10. In a left_join, which table’s rows are guaranteed to appear in the result regardless of matches in the other table?

Only the right table. Both tables equally. Only the left table. Rows from neither table are guaranteed.