[R] Change in behavior of compare statement
murdoch at stats.uwo.ca
Mon Sep 19 19:40:53 CEST 2005
On 9/19/2005 12:25 PM, Tomas Andersson wrote:
> Dear all,
> I have come across some Windows Script code which calls the
> "file.exists" function in R to check for the existence of a particular
> file on an R server. This is what the code looks like:
> // some useful code
> while (m_workspace.session.eval("file.exists(" + dataFile
> + ")") != "1");
What is this function m_workspace.session.eval? It's not a base
function. Perhaps its definition has changed?
> It appears that the behavior of this code is different when used with
> R version 2.1.1 compared to R version 1.9.1. If the compare statement
> s is changed from
> while (s != "1")
> while (s != "True")
> while !(s)
> the behavior of the code is the same with both versions of R.
> After reading the R documentation, I have not found any evidence that
> the original syntax (s != "1") is in any way recommended or supported
> (in version 2.1.1). Still, my questions are:
s != "1" is perfectly valid R code. It will evaluate to TRUE in at
least the following case:
as.character(s) is not an NA, but isn't "1".
s != "True" will evaluate to TRUE in most cases, unless s happens to
contain that exact string.
> 1. Is it possible that the syntax has been supported in older versions of R?
> 2. Is the reason for the recent change in behavior known and
> documented anywhere?
The syntax is fine, but it looks like a behaviour change in that
function m_workspace.session.eval. You'll need to ask the author of
that function what is happening.
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