Begin forwarded message:
From: Peter Dalgaard <pda...@gmail.com>
Date: August 15, 2010 3:43:31 PM EDT
To: phgrosj...@sciviews.org
Cc: r-help@r-project.org
Subject: Re: [R] as.logical(factor) behaviour
Philippe Grosjean wrote:
Thank you, but I already know that. I am not surprised by this
behavior,
but by an inconsistency between that behavior and the documentation
that
says "For factors, this uses the levels (labels).", which it does
not.
Best,
My gut feeling say that the docs need to be changes. The current
situation is a bit silly because de facto, as.logical(f) is always
TRUE
(except for NA handling). However, fixing the code to match the docs
would instead give NA in nearly all cases, and I suspect that has
potential to upset code all over the place.
It is easy enough to try and see what happens:
as.logical.factor <- function(x)as.logical(levels(x))[x]
as.logical(factor(0))
[1] NA
as.logical(factor(FALSE))
[1] FALSE
as.logical(factor(TRUE))
[1] TRUE
as.logical(factor(1))
[1] NA
as.logical("0")
[1] NA
What about changing it to behave thusly:
> as.logical.factor <- function(vec)
as.logical(as.numeric(factor(vec))-1 )
> as.logical(as.numeric(factor(c("TRUE", "FALSE", NA)))-1 )
[1] TRUE FALSE NA
> as.logical(as.numeric(factor(c(TRUE, FALSE, NA)))-1 )
[1] TRUE FALSE NA
--
David Winsemius, MD
West Hartford, CT
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