R Programming Language Certification Data Manipulation & Transformation 3

Question 1

Which function computes summary statistics for each group after group_by()?

Accepted Answer

summarise()

Answer

summarise() (or summarize()) computes one or more summary statistics for each group defined by group_by().

Question 2

What does the spread() function in tidyr (deprecated) do?

Accepted Answer

Converts long format to wide format

Answer

spread() (now replaced by pivot_wider()) converts a long-format data frame to wide format by spreading a key column into multiple columns.

Question 3

Which function in the purrr package applies a function to each element of a list and returns an atomic vector?

Accepted Answer

map_dbl()

Answer

map_dbl() applies a function to each element and returns a double (numeric) vector, enforcing type safety.

Question 4

In R, which function converts a data frame column to a factor?

Accepted Answer

as.factor()

Answer

as.factor() converts a vector or column to a factor type, representing categorical data with defined levels.

Question 5

Which dplyr function selects rows based on a condition?

Accepted Answer

filter()

Answer

filter() subsets rows of a data frame by keeping only those rows where the specified logical condition is TRUE.

R Programming Language Certification Practice Test