Reaction to the provided answer for Stackoverflow question at https://stackoverflow.com/q/35712196

expand_ballrooms.R

# There is really not a dynamic way of doing what you want.
# You will need to expand the dash and generate a sequence from it.
# I wrote an example function that converts something like 2-4 into seq(2, 4)

expand.dash <- function(dashed) {
    limits <- unlist(strsplit(dashed, '-'))
    seq(limits[1], limits[2])
}

# We can use the above function inside another function which expands ballrooms

expand.ballrooms <- function(txt) {
    str <- gsub('\\d+\\s*-\\s*\\d+', '%d', txt)
    dashed_str <- gsub('[a-zA-Z ]+', '', txt)
    sprintf(str, expand.dash(dashed_str))
}

# Use the paste0 function to combine the result from expand.ballrooms
paste0(expand.ballrooms('Ballroom 2-10'), collapse=', ')