[R] Using package ROCR

[wiener30]

I am trying to use package ROCR to analyze classification accuracy,
unfortunately there are some problems right at the beginning.

Question 1) 
When I try to run demo I am getting the following error message
> library(ROCR)
> demo(ROCR)
> if(dev.cur() <= 1) .... [TRUNCATED] 
Error in get(getOption("device")) : wrong first argument
When I issue the command
> dev.cur() 
it returns
null device 
          1
It seems something is wrong with my R-environment ?
Could somebody provide a hint, what is wrong.

Question 2)
When I run an example commands from the manual
library(ROCR)
data(ROCR.simple)
pred <- prediction( ROCR.simple$predictions, ROCR.simple$labels )
perf <- performance( pred, "tpr", "fpr" )
plot( perf )

the plot command issues the following error message
Error in as.double(y) : 
  cannot coerce type 'S4' to vector of type 'double'

How this could be fixed ?

Thanks for the support

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