R help - Sep 2004 - is.constant 2

>>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
 >}

Since the issue of factors surfaced, I improved my function:

is.constant <-  function(x) {
   if (is.factor(x)) (length(attributes(x)$levels)==1) && 
(!any(is.na(as.character(x))))
   else (is.numeric(x) && !any(is.na(x)) && identical(min(x),
max(x)))
}

  is.constant(rep(c(sin(pi/2),1),10)) # TRUE
  x <- factor(c(1,1,NA))
  is.constant(x)            # FALSE because of NA
  is.constant(x[1:2])       # TRUE
  is.constant(c(1,1,NA))    # FALSE because of NA
  is.constant(c(1,1,2))     # FALSE
  is.constant(c(1,1,1))     # 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)

Christian Hoffmann <christian.hoffmann <at> wsl.ch> writes:
> 
> >>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
>  >}
> 
> Since the issue of factors surfaced, I improved my function:
> 
> is.constant <-  function(x) {
>    if (is.factor(x)) (length(attributes(x)$levels)==1) && 
> (!any(is.na(as.character(x))))
>    else (is.numeric(x) && !any(is.na(x)) &&
identical(min(x), max(x)))
> }
Suggest you use an S3 generic and a separate methods for factor, and
in the future, other classes.  Also to make it more consistent with
other R functions have an na.rm= argument which defaults to TRUE.
If na.rm = FALSE then it should return NA  there are any NAs in
the same way that sum(c(1,2,NA), na.rm = FALSE) returns NA. There is 
some question of how to handle zero length arguments (or ones
that become zero length after removing NAs).

is.constant <- function(x, ...) UseMethod("is.constant")
is.constant.factor <- function(x, na.rm = TRUE) ... code for factor ...
is.constant.default <- function(x, na.rm = TRUE) ... code for default ...