[R] is.constant 2

[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
 >}

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)