The function partially sorts the elements so that identical values are
adjacent. NA
values come last. This is guaranteed to be
stable, so ties are preserved, and if the data are already
grouped/sorted, the grouping is unchanged. This is useful for
aggregation and is particularly fast for character vectors.
Under the covers, the "radix"
method of order
is
used, and the same caveats apply, including restrictions on character
encodings and lack of support for long vectors (those with
\(2^{31}\) or more elements). Real-valued numbers are slightly
rounded to account for numerical imprecision.
Like order
, for a classed R object the grouping is based on
the result of xtfrm
.