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