R Programming Language Certification R Programming Language: Computer Science 5

Question 1

In R's S3 object system, how does `UseMethod()` determine which method to call?

Accepted Answer

It dispatches based on the first element of class()

Answer

UseMethod() dispatches to a function named generic.classname using the first element of the object's class vector.

Question 2

Which R function serializes an R object to a binary format for saving to disk?

Accepted Answer

saveRDS()

Answer

saveRDS() saves a single R object to a binary .rds file that can be restored with readRDS().

Question 3

What does `Reduce('+', list(1,2,3,4))` return in R?

Accepted Answer

10

Answer

Reduce applies + cumulatively: ((1+2)+3)+4 = 10, returning the final scalar result.

Question 4

In R, what is a closure?

Accepted Answer

A function that captures its enclosing environment

Answer

A closure is a function bundled with a reference to its enclosing lexical environment at creation time.

Question 5

Which R function checks for duplicate rows in a data frame?

Accepted Answer

duplicated()

Answer

duplicated() returns a logical vector marking each row that is a duplicate of an earlier row.

R Programming Language Certification Practice Test