R version 2.15.0 (2012-03-30)
Copyright (C) 2012 The R Foundation for Statistical Computing
ISBN 3-900051-07-0
Platform: x86_64-unknown-linux-gnu (64-bit)

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> ## allow backticks in rpart.matrix: see
> ## https://stat.ethz.ch/pipermail/r-help/2012-May/314081.html
> 
> library(rpart)
> Iris <- iris
> names(Iris) <- sub(".", " ", names(iris), fixed=TRUE)
> rpart(Species ~ `Sepal Length`, data = Iris)
n= 150 

node), split, n, loss, yval, (yprob)
      * denotes terminal node

1) root 150 100 setosa (0.33333333 0.33333333 0.33333333)  
  2) Sepal Length< 5.45 52   7 setosa (0.86538462 0.11538462 0.01923077) *
  3) Sepal Length>=5.45 98  49 virginica (0.05102041 0.44897959 0.50000000)  
    6) Sepal Length< 6.15 43  15 versicolor (0.11627907 0.65116279 0.23255814) *
    7) Sepal Length>=6.15 55  16 virginica (0.00000000 0.29090909 0.70909091) *
> 
> proc.time()
   user  system elapsed 
  0.234   0.064   0.328