R Programming Language Certification Case Studies & Practical Application 3

Question 1

A genomics researcher stores RNA-seq count data in a matrix with 20,000 genes (rows) and 48 samples (columns). She needs row-wise means efficiently. Which approach is fastest in R?

Accepted Answer

rowMeans(mat)

Answer

rowMeans() is a vectorized C-level function specifically optimized for row means of matrices and is significantly faster than apply() or loops.

Question 2

An e-commerce company wants to segment customers into groups based on RFM (Recency, Frequency, Monetary) scores. After scaling the features, which R function performs k-means clustering?

Accepted Answer

kmeans(rfm_scaled, centers=5, nstart=25)

Answer

kmeans() performs k-means clustering; centers specifies k and nstart>1 runs multiple random initializations to find a better solution.

Question 3

A data engineer reads a 2GB CSV file into R and immediately hits memory limits. Which strategy reduces memory usage most effectively before processing?

Accepted Answer

Use data.table::fread() with select and colClasses to load only needed columns with correct types

Answer

fread() with select loads only the needed columns and colClasses prevents over-allocation from default type inference, minimizing RAM usage from the start.

Question 4

A social scientist is running a multi-level model (mixed effects) to account for students nested within schools. Which R package and function is most appropriate?

Accepted Answer

lmer() from the lme4 package with (1|school) as a random intercept

Answer

lme4's lmer() fits linear mixed-effects models; (1|school) specifies a random intercept for each school, correctly accounting for the nested structure.

Question 5

A sports analytics team scrapes game statistics from a website using rvest. After parsing, player names arrive as ' LeBron James  ' with extra whitespace. Which function cleans this?

Accepted Answer

Both B and C are correct

Answer

Both trimws() (base R) and stringr's str_trim() remove leading and trailing whitespace and produce identical results.

R Programming Language Certification Practice Test

R Programming Language Certification Practice Test

R Programming Language Certification Case Studies & Practical Application 3