Thanks for the help! Are you sure R version plays a role in this case? My R
version is 2.13.0

Your suggestion prompted me to look into the help content of ifelse, and a
similar example exists there:

     x <- c(6:-4)
     sqrt(x)  #- gives warning
     sqrt(ifelse(x >= 0, x, NA))  # no warning

     ## Note: the following also gives the warning !
     ifelse(x >= 0, sqrt(x), NA)

Based on the above example, now I have a solution for my situation:

tConvert2 <- function(tval, DF, fullDF) qt(pt(ifelse(DF>=1, tval, 0),
ifelse(DF>=1, DF, 1)), fullDF)

> tConvert2(c(2,3), c(0,12), 12)
[1] 0 3

However, I feel my solution is a little kludged. Any better idea?

Thanks,
Gang



On Thu, Jul 7, 2011 at 9:04 PM, David Winsemius <dwinsemius@comcast.net>wrote:

>
> On Jul 7, 2011, at 8:52 PM, David Winsemius wrote:
>
>
>> On Jul 7, 2011, at 8:47 PM, Gang Chen wrote:
>>
>>  I define the following function to convert a t-value with degrees of
>>> freedom
>>> DF to another t-value with different degrees of freedom fullDF:
>>>
>>> tConvert <- function(tval, DF, fullDF) ifelse(DF>=1, qt(pt(tval, DF),
>>> fullDF), 0)
>>>
>>> It works as expected with the following case:
>>>
>>>  tConvert(c(2,3), c(10,12), 12)
>>>>
>>> [1] 1.961905 3.000000
>>>
>>> However, it gives me warning for the example below although the output is
>>> still as intended:
>>>
>>>  tConvert(c(2,3), c(0,12), 12)
>>>>
>>> [1] 0 3
>>> Warning message:
>>> In pt(q, df, lower.tail, log.p) : NaNs produced
>>>
>>> I'm confused about the warning especially considering the fact that the
>>> following works correctly without such warning:
>>>
>>>  tConvert(2, 0, 12)
>>>>
>>> [1] 0
>>>
>>> What am I missing?
>>>
>>
>> The fact that ifelse evaluates both sides of the consequent and
>> alternative.
>>
>
> I also think you should update yur R to the most recent version since a
> current version does not issue that warning.
>
>
> --
> David Winsemius, MD
> West Hartford, CT
>
>

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