R Under development (unstable) (2013-12-04 r64388) -- "Unsuffered Consequences"
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Platform: x86_64-apple-darwin13.0.0 (64-bit)

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> library(foreign)
> 
> DF <- data.frame(X1 = 1:3, X2 = 4:6, X3 = paste0("str_", 1:3), 
+                  stringsAsFactors = FALSE)
> 
> write.foreign(DF, "datafile.dat", "codefile.sps", "SPSS")
> 
> files <- c( "datafile.dat", "codefile.sps")
> for(f in files) tools::Rdiff(f, file.path("keep", f))
> unlink(files)
> 
> proc.time()
   user  system elapsed 
  0.223   0.031   0.239