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A general description is here.
Radix sort is now the ‘"auto"’ algorithm for ‘sort.int()’ for double vectors (and hence used for ‘sort()’ for unclassed double vectors), excluding ‘long’ vectors.
‘sort.int(method = "radix")’ no longer rounds double vectors.
The ‘default’ and ‘data.frame’ methods for ‘stack()’ preserve the names of empty elements in the levels of the ‘ind’ column of the return value. Set the new ‘drop’ argument to ‘TRUE’ for the previous behavior.
The deprecated support for PCRE versions 8.10 to 8.31 will be removed
prior to R 3.4.0.