Sort a Data Frame

sort.df <-  function(d)
{ 
    ## Purpose: Sort a Data Frame along 1st column, ties along 2nd, ..., until its last column. 
    ## Arguments:
    ##   d: a data frame
    ## Return: a sorted data frame
    ## Author: Feiming Chen, Date: 18 Apr 2017, 13:49
    ## ________________________________________________
    d[ do.call(order, d), ]    
}
if (F) {                                # Unit Test
    df <- data.frame(X = c("b", "a", "a", "c"), Y = c(4, 2, 1, 3))
    sort.df(df)
    ##   X Y
    ## 3 a 1
    ## 2 a 2
    ## 1 b 4
    ## 4 c 3

    sort.df(df[2:1])
    ##   Y X
    ## 3 1 a
    ## 2 2 a
    ## 4 3 c
    ## 1 4 b
}