--- a/r.rst	Sun Mar 06 00:27:25 2016 +0200
+++ b/r.rst	Sun Mar 06 00:28:56 2016 +0200
@@ -227,3 +227,7 @@
 
   newdf <- df[ , !(names(df) %in% c("lat", "long"))]
 
+  df <- data.frame( a = 1:10, b = 2:11, c = 3:12 )
+  df <- subset(df, select = c(a,c))
+  df <- subset(df, select = -c(a,c))
+