Reading and writing vectors of values (low-level)

The three functions get.ff, set.ff and getset.ff provide the simplest interface to access an ff file: getting and setting vector of values identified by positive subscripts

Usage

get.ff(x, i)
set.ff(x, i, value, add = FALSE)
getset.ff(x, i, value, add = FALSE)

Arguments

x: an ff object
i: an index position within the ff file
value: the value to write to position i
add: TRUE if the value should rather increment than overwrite at the index position

Details

getset.ff combines the effects of get.ff and set.ff in a single operation: it retrieves the old value at position i before changing it. getset.ff will maintain na.count.

Value

get.ff returns a vector, set.ff returns the 'changed' ff object (like all assignment functions do) and getset.ff returns the value at the subscript positions. More precisely getset.ff(x, i, value, add=FALSE) returns the old values at the subscript positions i while getset.ff(x, i, value, add=TRUE) returns the incremented values at the subscript positions.

Author

Jens Oehlschlägel

Note

get.ff, set.ff and getset.ff are low level functions that do not support ramclass and ramattribs and thus will not give the expected result with factor and POSIXct

Examples

 x <- ff(0, length=12)
 get.ff(x, 3L)
#> [1] 0
 set.ff(x, 3L, 1)
#> ff (open) double length=12 (12)
#>  [1]  [2]  [3]  [4]  [5]  [6]       [7]  [8]  [9] [10] [11] [12] 
#>    0    0    1    0    0    0    :    0    0    0    0    0    0 
 x
#> ff (open) double length=12 (12)
#>  [1]  [2]  [3]  [4]  [5]  [6]       [7]  [8]  [9] [10] [11] [12] 
#>    0    0    1    0    0    0    :    0    0    0    0    0    0 
 set.ff(x, 3L, 1, add=TRUE)
#> ff (open) double length=12 (12)
#>  [1]  [2]  [3]  [4]  [5]  [6]       [7]  [8]  [9] [10] [11] [12] 
#>    0    0    2    0    0    0    :    0    0    0    0    0    0 
 x
#> ff (open) double length=12 (12)
#>  [1]  [2]  [3]  [4]  [5]  [6]       [7]  [8]  [9] [10] [11] [12] 
#>    0    0    2    0    0    0    :    0    0    0    0    0    0 
 getset.ff(x, 3L, 1, add=TRUE)
#> [1] 3
 getset.ff(x, 3L, 1)
#> [1] 3
 x
#> ff (open) double length=12 (12)
#>  [1]  [2]  [3]  [4]  [5]  [6]       [7]  [8]  [9] [10] [11] [12] 
#>    0    0    1    0    0    0    :    0    0    0    0    0    0 
 rm(x); gc()
#>           used (Mb) gc trigger  (Mb) max used  (Mb)
#> Ncells 1250008 66.8    2239654 119.7  2239654 119.7
#> Vcells 2301070 17.6    8388608  64.0  8387257  64.0