mix.R

    base <- paste("plot",set,group,id,suff,sep="_")
    fn <- paste0(base,".",ext)
    fn <- gsub("\\[","",fn)
    fn <- gsub("\\]","",fn)
    fn <- gsub("\\+","p",fn)
    fn <- gsub("-","m",fn)
    if (!is.null(top)) file.path(top,fn) else fn
}