[R] Unexpected returned value from a function

[Dan Davison]

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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-- 
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