R Programming Language Certification Case Studies & Practical Application 4

Question 1

A cybersecurity analyst has a character vector of IP addresses and needs to extract only those matching IPv4 format (e.g., '192.168.1.1'). Which base R function uses a regex for this?

Accepted Answer

grep('^(\d{1,3}\.){3}\d{1,3}$', ips, value=TRUE)

Answer

grep() with value=TRUE returns matching elements; the regex anchors to start and end and matches the four-octet IPv4 pattern.

Question 2

An economist fits a multiple linear regression and suspects heteroskedasticity after plotting residuals vs. fitted values. Which test formally checks for heteroskedasticity in R?

Accepted Answer

bptest() from the lmtest package (Breusch-Pagan test)

Answer

The Breusch-Pagan test (bptest() in lmtest) formally tests whether residual variance is constant across fitted values.

Question 3

A data journalist wants to create a choropleth map of US state unemployment rates using ggplot2. After joining unemployment data to a spatial data frame, which geom renders filled polygons for each state?

Accepted Answer

geom_sf(aes(fill=unemployment_rate))

Answer

geom_sf() renders simple features (sf) spatial objects and respects their geometry automatically, making it the modern standard for maps in ggplot2.

Question 4

A clinical trial statistician needs to perform a two-sample t-test assuming unequal variances (Welch's t-test) in R. Which call is correct?

Accepted Answer

t.test(group1, group2, var.equal=FALSE)

Answer

t.test() defaults to Welch's (var.equal=FALSE), which does not assume equal variances and is appropriate when variance homogeneity is uncertain.

Question 5

A DevOps engineer uses R to automate parsing server log files and needs to read each line of a 500MB log without loading the entire file into memory. Which approach is correct?

Accepted Answer

con <- file('server.log'); open(con); while(length(line <- readLines(con, n=1)) > 0) { ... }; close(con)

Answer

Opening a connection and reading n=1 line at a time processes the file sequentially without loading it fully into memory.

R Programming Language Certification Practice Test

R Programming Language Certification Practice Test

R Programming Language Certification Case Studies & Practical Application 4