phylotree/src/metrics/sackins.js

A JavaScript library for developing applications and interactive visualizations involving [phylogenetic trees](https://en.wikipedia.org/wiki/Phylogenetic_tree), written as an extension of the [D3](http://d3js.org) [hierarchy layout](https://github.com/d3/

import * as _ from "underscore";

/*
 * The Sackin's index is computed as the sum of the number of ancestors for each
 * tips of the tree.
 *
 * The less balanced a tree is, the larger its Sackin's index.
 *
 */

export default function sackin(tree) {

  // Get tips of tree
  let tips = tree.getTips();

  // Count number of ancestors to root for each tree
  let depths = _.map(tips, d => { return d.depth });

  return _.reduce(depths, function(memo, num){ return memo + num; }, 0);

}