Convert an ff POSIXct vector to an ff numeric vector

Question

I am trying to convert an ff vector with POSIXct entries to an ff numeric vector, containing the respective number of seconds since the origin 01-01-1970.

x = as.ff(as.POSIXct(c("2014-06-30 00:01:27 BST", "2014-06-30 00:02:17 BST")))

The 'natural' as.numeric(x) does not work, yielding: numeric(0).

as.ff(as.numeric(x[])) works, yielding

ff (open) double length=2 (2) [1] [2] 1398898887 1398898937

which is the desirable outcome. Albeit, it involves the ram object x[]. Is there a way to achieve the above result employing ff objects only (i.e. not intermediating the ram equivalent of the ff vector)?

Answer 1

require(ff)
x = as.ff(as.POSIXct(c("2014-06-30 00:01:27 BST", "2014-06-30 00:02:17 BST")))
## Either clone it (creates a duplicate of the ff file)
done <- clone(x, ramclass = "numeric", ramattribs = list())
done[]
[1] 1404079287 1404079337
attr(,"class")
[1] "numeric"

## Or just modify the ramclass and ramattribs (see ?virtual: virtual(x))
virtual(x)$ramclass <- NULL
virtual(x)$ramattribs <- NULL
x[]
[1] 1404079287 1404079337

## And wrap this up in your own function