Rank Biased Overlap (Base) implementation (javascript)

rbo.js

// http://blog.mobile.codalism.com/research/papers/wmz10_tois.pdf

// used for a list of 50 items
const P_VALUE = 0.8;

export const intersection = (a, b) => a.filter(x => b.indexOf(x) > -1);

export const overlap = (a, b) => intersection(a, b).length;

export const agreement = (a, b) => overlap(a, b) / a.length;

// used for comparing two indefinite ordinal lists
// RBO(base) = (1 - p) * sum{ p^(d-1) * agreement(a[0..d], b[0..d]) }
export const rankBiasedOverlap = (a, b) => {
  const sum = a.reduce((memo, _v, d) => {
    const p = P_VALUE ** d;
    const agg = agreement(a.slice(0, d + 1), b.slice(0, d + 1));
    return memo + (p * agg);
  }, 0);
  return parseFloat(((1 - P_VALUE) * sum).toFixed(4));
};