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A general description is here.
64-bit Windows builds of R are by default limited in memory usage to the amount of RAM installed: this limit can be changed by command-line option ‘--max-mem-size’ or setting environment variable ‘R_MAX_MEM_SIZE’.
‘sort()’, ‘sort.int()’ and ‘sort.list()’ now use radix sorting for factors of less than 100,000 levels when ‘method’ is not supplied.
‘order()’ for a single input calls ‘sort.list()’ and so uses radix sorting for most factors.
‘diag()’ as used to generate a diagonal matrix has been re-written in C for speed and less memory usage. It now forces the result to be numeric in the case ‘diag(x)’ since it is said to have ‘zero off-diagonal entries’.
What can be done with such vectors is currently somewhat limited, and
most operations will return the error ‘long vectors not supported yet’.
They can be serialized and unserialized, coercion, ‘identical()’ and
‘object.size()’ work and means can be computed.
Most operations which can sensibly be done with long vectors now work: others may return the error ‘long vectors not supported yet’. Some of these are because they explicitly work with integer indices (e.g. ‘anyDuplicated()’, ‘match()’, ‘sample.int()’) or because other limits (e.g. of character strings or matrix dimensions) would be exceeded or the operations would be extremely slow.
All aspects are currently experimental.
‘sort.list(method = "radix")’ could give incorrect results on certain compilers (seen with ‘clang’ on Mac OS 10.7 and ‘Xcode 4.4.1’).