# Sort a dataframe and display in a spreadsheet form, e.g.:
# sort.df(my_df, c("var1", "var2"))
show.df=function (data, vars = names(data)) 
{
    if (length(vars) == 0 || is.null(vars)) 
        return(data)
    invisible(edit(data[do.call("order", data[, vars, drop = FALSE]), , drop = FALSE]))
}