[R] T.test error help

[Uwe Ligges]

Daniel Malter wrote:
> put another condition in your loop
> 
> if(all.equal(x,y)=TRUE) i=i+1 else t.test...
> 
> something in that direction.


Sorry, but that's neither valid R code nor sensible in this case.
See my suggestions below.




> best,
> daniel 
> 
> 
> -------------------------
> cuncta stricte discussurus
> -------------------------
> 
> -----Ursprüngliche Nachricht-----
> Von: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] Im
> Auftrag von Amit Patel
> Gesendet: Thursday, July 09, 2009 9:20 AM
> An: r-help at r-project.org
> Betreff: [R] T.test error help
> 
> 
> 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])) {


for(i in seq_along(zz[,1])){

should be safer.


> 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, you can wrap it in try() and check the object with
if(inherits(object, "try-error")) later on in order to do something 
different (e.g. assign an NA) in case of an error.

Uwe Ligges


> 
> 
> 
> 
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