Question

I have a task in which I have a labeled numeric vector, say size 5 and labels a, b, c, d, e, and I need to sort it and then print the labels in (inverse) sorted order. So for example, given this vector v1 in input:

     a   b    c   d     e
1   -3  -1   10   5   -15

the required output would be: cdbae.

Now, the hard part is handling ties. I need to print all possible orders in case of a tie. So for example, given this other vector v2 in input:

     a    b    c    d    e
1   10   29   10   10  -15

After sorting we’d have:

     b    a   c    d    e
1   29   10  10   10  -15

But of course we have 3! = 6 possible permutations. I would like it to print this array:

v <- c("bacde", "badce", "bcade", "bcdae", "bdcae", "bdace").

If that helps, the number of labels is never more than 10 so I don’t mind performance relative to that, for that matter.

Answer 1

This does it. But I wouldn’t recommend running on dataset with too many ties.

require(gregmisc)
x <- c(a=10, b=29, c=10, d=10, e=-15)
y <- sort(x, decreasing=T)

if (any(duplicated(y))) {
    o <- sapply(unique(y), function(val) {
        m <- names(y[y==val])
        # just to make things quicker using length(m)
        if (length(m) <= 1) {
            return(m)
        }
        do.call(paste0, as.data.frame(permutations(length(m), length(m), m)))
    })
    out <- do.call(paste0, expand.grid(o))
} else {
    out <- paste(names(y), collapse="")
}

# [1] "bacde" "badce" "bcade" "bcdae" "bdace" "bdcae"

Of course it handles multiple ties as well. Running on:

x <- c(a=10, b=29, c=10, d=-10, e=35, f=-10, g=10)
y <- sort(x, decreasing = TRUE)

gives:

# [1] "ebacgdf" "ebagcdf" "ebcagdf" "ebcgadf" "ebgacdf" "ebgcadf" "ebacgfd" "ebagcfd"
# [9] "ebcagfd" "ebcgafd" "ebgacfd" "ebgcafd"