[R] is.constant
Liaw, Andy
andy_liaw at merck.com
Wed Sep 22 12:31:31 CEST 2004
> Christian Hoffmann
>
> >>x <- c(1, 2, NA)
> >>is.constant(x)
> >
> > [1] TRUE
> >
> > For data such as c(1, 1, 1, NA), I should think the safest
> answer should be
> > NA, because one really doesn't know whether that last
> number is 1 or not.
> >
> > Andy
> >
> My version is
> is.constant <- function(x) {
> if (is.numeric(x) & !any(is.na(x))) identical(min(x),
> max(x)) else FALSE
> }
>
> rendering
> > is.constant(c(1,1,NA))
> [1] FALSE
As I said, the `safest' thing is to return NA, as the NA could be 1, or it
could be something else. We just don't know. It's probably a cleaner style
to have is.constant() return NA in the case that the input contains contants
and some NAs, and TRUE or FALSE otherwise; e.g., is.constant(c(1,2,NA))
should clearly be FALSE. Then the output of is.constant() should be checked
for possible NA.
Just my $0.02...
Andy
> > is.constant(c(1,1,NaN))
> [1] FALSE
> > is.constant(rep(c(sin(pi/2),1),10)) # TRUE
> [1] TRUE
> --
> Dr.sc.math.Christian W. Hoffmann,
> http://www.wsl.ch/staff/christian.hoffmann
> Mathematics + Statistical Computing e-mail:
> christian.hoffmann at wsl.ch
> Swiss Federal Research Institute WSL Tel: ++41-44-73922-
> -77 (office)
> CH-8903 Birmensdorf, Switzerland -11(exchange), -15 (fax)
>
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