R : Copyright 2006, The R Foundation for Statistical Computing
Version 2.3.1 (2006-06-01)
ISBN 3-900051-07-0

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> # Goal: To do sorting.
> #
> # The approach here needs to be explained. If `i' is a vector of
> # integers, then the data frame D[i,] picks up rows from D based
> # on the values found in `i'.
> #
> # The order() function makes an integer vector which is a correct
> # ordering for the purpose of sorting.
> 
> D <- data.frame(x=c(1,2,3,1), y=c(7,19,2,2))
> D
  x  y
1 1  7
2 2 19
3 3  2
4 1  2
> 
> # Sort on x
> indexes <- order(D$x)
> D[indexes,]
  x  y
1 1  7
4 1  2
2 2 19
3 3  2
> 
> # Print out sorted dataset, sorted in reverse by y
> D[rev(order(D$y)),]
  x  y
2 2 19
1 1  7
4 1  2
3 3  2
>