[R] Unexpected returned value from a function
Dan Davison
davison at stats.ox.ac.uk
Wed Sep 17 00:50:53 CEST 2008
What you want is
ConvertMissingToNA <- function (values) {
values[ values == -9999 | values == -999999] <- NA
return( values )
}
To see why your version doesn't do what you wanted, maybe it helps to
consider the following?
x <- 1:10
y <- (x[3:6] <- 99)
y ## 99
(It's perhaps not entirely obvious that the value of y should be 99
and not c(99,99,99,99), but anyway, neither correspond to what you
wanted.)
Dan
On Tue, Sep 16, 2008 at 03:19:53PM -0700, Hutchinson,David [PYR] wrote:
> Hi R-Users,
>
> I wrote a simple function to change values of a matrix or vector to NA
> based on the element value being -9999 or -999999. I don't understand
> why the function returns a unit vector (NA) instead of setting all
> values in the vector which have -9999 or -999999 to NA. When I apply the
> function in line, it appears to work correctly?
>
> Can someone enlighten me what I am doing wrong?
>
> Thanks in advance.
>
> David
>
>
> Here's my example:
>
>
> ConvertMissingToNA <- function (values) {
> return ( values[ values == -9999 | values == -999999] <- NA )
> }
>
> d <- floor(runif(10, 1, 100))
> pos <- floor (runif(5, 1, 10))
> d[pos] <- -9999
> pos <- floor (runif(2, 1, 10))
> d[pos] <- -999999
> print (d)
>
> # now apply function
> e <- ConvertMissingToNA (d) # will return NA as a unit vector
> print (e)
>
> # conduct function in-line
> d[ d == -9999 | d == -999999] <- NA # correctly converts values to NA
> print (d)
>
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--
http://www.stats.ox.ac.uk/~davison
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