On Jul 7, 2011, at 10:17 PM, Gang Chen wrote:
Thanks for the help! Are you sure R version plays a role in this
case? My R version is 2.13.0
I'm not sure, but my version is 2.13.1
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
The x variable gets converted to c( 6:0, NA,NA,NA, NA)
Notice the differences here:
> sqrt(NA)
[1] NA
> sqrt(-1)
[1] NaN
Warning message:
In sqrt(-1) : NaNs produced
> qt(.5, 0)
[1] NaN
Warning message:
In qt(p, df, lower.tail, log.p) : NaNs produced
> qt(.5, NA)
[1] NA
## 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 <dwinsem...@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
David Winsemius, MD
West Hartford, CT
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