data.table (version 1.7.1)
Extension of data.frame for fast indexing, fast ordered joins,
fast assignment, fast grouping and list columns.
Description
Enhanced data.frame. Fast indexing, fast ordered joins,
fast assignment, fast grouping and list columns in a short and
flexible syntax. i and j may be expressions of column names
directly, for faster development. Example: X[Y] is a fast join
for large data.