Categories / data.table
Incremental Counter within DataFrame only When a Condition is Met in R Using cumsum() with factor() and as.integer().
Assignment by Reference in R's Data Table: A Common Pitfall to Avoid When Aggregating Data
Removing Grouping Variables with R: Efficient Data Table Wrangling Strategies
Mastering the `%between%` Function in `data.table`: A Guide to Efficient Data Subseting