R Programming Language Certification R Programming Language: Computer Science 3

Question 1

Which R function applies a function to each element of a list and returns a list?

Accepted Answer

lapply()

Answer

lapply() always returns a list, unlike sapply() which attempts simplification.

Question 2

What does the `<<-` operator do in R?

Accepted Answer

Assigns a value in the global or enclosing environment

Answer

<<- performs assignment in the parent (enclosing) environment, bypassing the current local scope.

Question 3

In R, `Sys.time()` returns an object of which class?

Accepted Answer

POSIXct POSIXt

Answer

Sys.time() returns a POSIXct object representing the current date-time as seconds since the Unix epoch.

Question 4

Which function converts a character vector to lowercase in R?

Accepted Answer

tolower()

Answer

tolower() is the base R function for converting strings to lowercase.

Question 5

What is the default `stringsAsFactors` behavior in R 4.0+ when using `data.frame()`?

Accepted Answer

FALSE — strings remain character vectors

Answer

Since R 4.0, stringsAsFactors defaults to FALSE, keeping character columns as character vectors.

R Programming Language Certification Practice Test