将ff POSIXct向量转换为ff数字向量

Question

我正在尝试将ff向量与POSIXct条目转换为ff数值向量，其中包含自原点01-01-1970年以来的相应秒数。

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

“自然”as.numeric(x)不起作用，结果是：numeric(0)。

as.ff(as.numeric(x[]))工作，产量

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

这是理想的结果。尽管如此，它涉及到ram对象x[]。是否有方法仅使用ff对象(即不中介ff向量的ram等价)来实现上述结果？

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