Mario works with a group of R programmers tasked with copying data from an accounting system into a data warehouse. In what phase are the group's R skills most relevant?

The Extract phase focuses on retrieving data from source systems, which typically involves connectors or scripts to pull raw data, not extensive R programming.

The Load phase involves inserting the transformed data into the data warehouse, which often uses database-specific utilities or scripts for efficient bulk loading, rather than R's primary strengths.

The Transform phase of ETL involves data cleaning, filtering, aggregation, and restructuring to fit the data warehouse schema; R's strong capabilities in statistical computing and data manipulation are highly valuable for these tasks.

Purge is not a standard phase in the core ETL process; it refers to deleting old or unwanted data, which is a maintenance task rather than a core data integration step.