Hi,
On Jul 9, 2009, at 9:19 AM, Amit Patel wrote:
Hi I am implementing the t.test in a loop and where the data is the
same i get an error message.
Error in t.test.default(Samp3, Samp1, na.rm = TRUE, var.equal =
FALSE, :
data are essentially constant
The script i am using is
for (i in 1:length(zz[,1])) {
Samp1 <- zz[i,2:17]
Samp2 <- zz[i,18:33]
Samp3 <- zz[i,34:47]
Samp4 <- zz[i,48:63]
TTestResult[i,2] <- t.test(Samp2, Samp1, na.rm=TRUE, var.equal =
FALSE, paired=FALSE, conf.level=0.95)$p.value
TTestResult[i,3] <- t.test(Samp3, Samp1, na.rm=TRUE, var.equal =
FALSE, paired=FALSE, conf.level=0.95)$p.value
TTestResult[i,4] <- t.test(Samp4, Samp1, na.rm=TRUE, var.equal =
FALSE, paired=FALSE, conf.level=0.95)$p.value
}
Is there a way to make my loop ignore this problem and go onto the
next iteration
Yes, see: ?try and ?tryCatch
For example:
R> log(10)
[1] 2.302585
R> log("a")
Error in log("a") : Non-numeric argument to mathematical function
R> a <- tryCatch(log(10), error=function(e) {
+ cat("There was an error\n")
+ NA
+ })
R> b <- tryCatch(log("a"), error=function(e) {
+ cat("There was an error\n")
+ NA
+ })
There was an error
R> a
[1] 2.302585
R> b
[1] NA
-steve
--
Steve Lianoglou
Graduate Student: Physiology, Biophysics and Systems Biology
Weill Medical College of Cornell University
Contact Info: http://cbio.mskcc.org/~lianos
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