Message-ID: <432F2421.3030608@stats.uwo.ca>
Date: 2005-09-19T20:48:33Z
From: Duncan Murdoch
Subject: Change in behavior of compare statement
In-Reply-To: <432EF825.9070706@stats.uwo.ca>
On 9/19/2005 1:40 PM, Duncan Murdoch wrote:
> 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:
>>
>> do
>> {
>> // 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?
This has to be one of the most out-to-lunch answers I ever wrote.
Sorry, please ignore it.
The code above is "Windows Script", whatever that is, not R.
file.exists hasn't changed, but whatever interface you're using to R
presumably has. In the code you're looking at there, it converted TRUE
to "1", and now it doesn't.
Duncan Murdoch
>>
>> 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")
>> to
>> while (s != "True")
>> or
>> 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.
>
> Duncan Murdoch
>