list parentless nodes in ontology_index instance
Examples
onto_roots
#> function (x)
#> {
#> roots = x$id[sapply(x$parents, length) == 0]
#> show_roots <- roots[order(sapply(x$children[roots], length),
#> decreasing = TRUE)]
#> cat(paste0(collapse = "", "\t", show_roots, " - ", x$name[show_roots],
#> "\n"), sep = "")
#> }
#> <bytecode: 0x1782630a8>
#> <environment: namespace:ontoProc>