data.table (version 1.4.1)
Extension of data.frame for fast subset, fast merge and fast
grouping.
Description
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).