metric
Metric is a set of metric (distance) functions, along with assorted related functions such as similarity and preference functions, with a variety of interfaces.
Metric Functions
.rd1 (x,y)

.rd2 (x,y)

Non Metric, Related functions
.similar (other,self)
other and self are floating point, returns 0 to 1, 1 being the most similar
.similarKey (other, self, key)
other and self are objects, executes similarityFn on the key
example:
john = { score: 24, name: "John Doe" };
bill = { score: 20, name: "Bill Smith" };
var sim = require('metric').similarityFnKey;
console.log(sim(john,bill,'score'));
>> 0.8 // 80% similar