[R] Trap an error from a function

[David Winsemius]

On Sep 18, 2012, at 5:10 PM, John Sorkin wrote:

> Window 7
> R 2.15
> 
> I am writing a simulation which generates sample sized estimates from simulated data. When I run the function shown below,
> power.t.test(delta=14.02528,sd=1.945226,power=0.8,sig.level=0.05)
> 
> I get an error message:
> 
>> power.t.test(delta=14.02528,sd=1.945226,power=0.8,sig.level=0.05)
> Error in uniroot(function(n) eval(p.body) - power, c(2, 1e+07)) : 
>  f() values at end points not of opposite sign
> 
> The fact that the function can not return a sample size is OK, however I need to trap the error and set the sample size equal to NA. How do I trap the error so that when the error occurs I can set sample size equal to NA? 

?conditions   #### has lots of fancy stuff
# But I use just plain old `try`

test=-10:10
sapply(test, function(x)  if( "try-error" %in% 
                     class( try( test[test[x:1]] ) ) ){
                     2}else{0} )
Error in test[x:1] : only 0's may be mixed with negative subscripts
Error in test[x:1] : only 0's may be mixed with negative subscripts
Error in test[x:1] : only 0's may be mixed with negative subscripts
Error in test[x:1] : only 0's may be mixed with negative subscripts
Error in test[x:1] : only 0's may be mixed with negative subscripts
Error in test[x:1] : only 0's may be mixed with negative subscripts
Error in test[x:1] : only 0's may be mixed with negative subscripts
Error in test[x:1] : only 0's may be mixed with negative subscripts
Error in test[x:1] : only 0's may be mixed with negative subscripts
Error in test[x:1] : only 0's may be mixed with negative subscripts
 [1] 2 2 2 2 2 2 2 2 2 2 0 0 0 0 0 0 0 0 0 0 0

You still get the messages but the code runs.

-- 

David Winsemius, MD
Alameda, CA, USA