R: Getting attribute values as a vector
I have a object with some attributes whose values are integers, i.e. h =
:
attr(,"foo")
[1] 4
attr(,"bar")
[1] 2
An开发者_运维知识库d I want to get vector of type integer(2)
, v =
:
[1] 4 2
I have found two clumsy ways to achieve this
as.vector(sapply(names(attributes(h)), function(x) attr(h, x)))
or:
as.integer(paste(attributes(h)))
The solution I am looking for just needs to work for the basic case I described above and needs to be as fast as possible.
Well, if you can live with the names intact:
> h <- structure(42, foo=4, bar=2)
> unlist(attributes(h))
foo bar
4 2
Otherwise (which is actually faster!),
> unlist(attributes(h), use.names=FALSE)
[1] 4 2
The performance is as follows:
system.time( for(i in 1:1e5) unlist(attributes(h)) ) # 0.39 secs
system.time( for(i in 1:1e5) unlist(attributes(h), use.names=FALSE) ) # 0.25 secs
system.time( for(i in 1:1e5) as.integer(paste(attributes(h))) ) # 1.11 secs
system.time( for(i in 1:1e5) as.vector(sapply(names(attributes(h)),
function(x) attr(h, x))) ) # 6.17 secs
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