Dealing with TRUE, FALSE, NA and NaN

Question

Here is a vector

a <- c(TRUE, FALSE, FALSE, NA, FALSE, TRUE, NA, FALSE, TRUE)

I'd like a simple function that returns TRUE everytime there is a TRUE in "a", and FALSE everytime there is a FALSE or a NA in "a".

The three following things do not work

a == TRUE
identical(TRUE, a)
isTRUE(a)

Here is a solution

a[-which(is.na(a))]

but it doesn't seem to be a straightforward and easy solution

Is there another solution ?

Here are some functions (and operators) I know:

identical()
isTRUE()
is.na()
na.rm()
&
|
!

• What are the other functions (operators, tips, whatever,...) that are useful to deal with TRUE, FALSE, NA, NaN?

• What are the differences between NA and NaN?

• Are there other "logical things" than TRUE, FALSE, NA and NaN?

Thanks a lot !

Answer 1

To answer your questions in order:

1) The == operator does indeed not treat NA's as you would expect it to. A very useful function is this compareNA function from r-cookbook.com:

  compareNA <- function(v1,v2) {
    # This function returns TRUE wherever elements are the same, including NA's,
    # and false everywhere else.
    same <- (v1 == v2)  |  (is.na(v1) & is.na(v2))
    same[is.na(same)] <- FALSE
    return(same)
   }

2) NA stands for "Not available", and is not the same as the general NaN ("not a number"). NA is generally used for a default value for a number to stand in for missing data; NaN's are normally generated because a numerical issue (taking log of -1 or similar).

3) I'm not really sure what you mean by "logical things"--many different data types, including numeric vectors, can be used as input to logical operators. You might want to try reading the R logical operators page: http://stat.ethz.ch/R-manual/R-patched/library/base/html/Logic.html.

Hope this helps!