This GNU R package provides bitmapped vectors of booleans (no NAs),
coercion from and to logicals, integers and integer subscripts; fast
boolean operators and fast summary statistics. With 'bit' vectors you
can store true binary booleans {FALSE,TRUE} at the expense of 1 bit
only, on a 32 bit architecture this means factor 32 less RAM and ~
factor 32 more speed on boolean operations. Due to overhead of R calls,
actual speed gain depends on the size of the vector: expect gains for
vectors of size > 10000 elements. Even for one-time boolean operations
it can pay-off to convert to bit, the pay-off is obvious, when such
components are used more than once.
.
Reading from and writing to bit is approximately as fast as accessing
standard logicals - mostly due to R's time for memory allocation. The
package allows one to work with pre-allocated memory for return values
by calling .Call() directly: when evaluating the speed of C-access with
pre-allocated vector memory, coping from bit to logical requires only
70% of the time for copying from logical to logical; and copying from
logical to bit comes at a performance penalty of 150%. the package now
contains further classes for representing logical selections: 'bitwhich'
for very skewed selections and 'ri' for selecting ranges of values for
chunked processing. All three index classes can be used for subsetting
'ff' objects (ff-2.1-0 and higher).
