R Programming Language Certification Case Studies & Practical Application 5

Question 1

An urban planner uses R to analyze bike-share trip data and needs to calculate trip duration in minutes from two POSIXct columns (start_time and end_time). Which expression is correct?

Accepted Answer

as.numeric(difftime(end_time, start_time, units='mins'))

Answer

difftime() with units='mins' computes the difference and as.numeric() converts the difftime object to a plain numeric value in minutes.

Question 2

A NLP researcher tokenizes customer reviews and builds a document-term matrix. After TF-IDF weighting, she wants to reduce dimensions before clustering. Which R function performs PCA?

Accepted Answer

prcomp(dtm_tfidf, scale.=TRUE)

Answer

prcomp() performs PCA; scale.=TRUE standardizes variables before decomposition, which is important when features are on different scales.

Question 3

A supply chain analyst has daily demand data and fits an ARIMA model using the forecast package. After fitting, which function generates a 30-day ahead point forecast with prediction intervals?

Accepted Answer

forecast(fit, h=30)

Answer

forecast() from the forecast package generates h-step-ahead forecasts with confidence intervals directly from an ARIMA (or other) fitted model object.

Question 4

A survey researcher has a Likert-scale response coded 1-5 stored as integer but wants to treat it as an ordered factor for analysis. Which call creates an ordered factor correctly?

Accepted Answer

Both B and C are correct depending on whether numeric or label levels are used

Answer

Both factor() with ordered=TRUE and ordered() create ordered factors; the choice depends on whether numeric codes or character labels are stored.

Question 5

A data engineer needs to write a data frame to a PostgreSQL database from R without loading the entire table to check for conflicts. Which package and function perform efficient bulk inserts?

Accepted Answer

DBI::dbWriteTable(con, 'table_name', df, append=TRUE)

Answer

DBI::dbWriteTable() with append=TRUE efficiently bulk-inserts rows into an existing PostgreSQL table without overwriting it.

R Programming Language Certification Practice Test

R Programming Language Certification Practice Test

R Programming Language Certification Case Studies & Practical Application 5