Extension of data.frame. i and j expressions, keys and binary search.
Like a data.frame but i and j may be expressions evaluated within the frame. i is then like base::with and j like select in base::subset. When i is itself a data.table, a join is invoked similar to base::merge but uses binary search on the sorted key.

Extension of data.frame for fast subset, fast merge and fast
grouping.
Matthew Dowle with many contributions from Tom Short.  See SVN
logs on R-Forge.
Enhanced data.frame. Fast subset, grouping and merge in a
short and flexible syntax. i and j may be expressions of column
names directly, for faster development.  Example:
data[a>3,sum(b*c),by=d] where data has 4 columns (a,b,c,d).

M Dowle and T Short
<datatable-help@lists.r-forge.r-project.org>
Enhanced data.frame. Fast subset, grouping and merge 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.

Extension of data.frame for fast indexing, fast ordered joins
and fast grouping.
Enhanced data.frame. Fast indexing, fast ordered joins and
fast grouping 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.

Enhanced data.frame. Fast indexing, fast ordered joins,
fast assignment and fast grouping 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.

Extension of data.frame for fast indexing, fast ordered joins,
fast assignment, fast grouping and list columns.
chron, ggplot2, plyr, testthat (>= 0.4), hexbin
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.

chron, ggplot2, plyr, reshape, testthat (>= 0.4), hexbin

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.