Merge pull request #827 from null-a/multimodality-test

Handle multimodality in sampler tests

src/math/statistics.js

@@ -2,6 +2,7 @@
 
 var _ = require('lodash');
 var assert = require('assert');
+var util = require('../util');
 
 var abs = Math.abs,
     pow = Math.pow,
@@ -78,7 +79,14 @@ function kde(samps, kernel) {
 function mode(samps) {
   // tally values and sort
   var tallied = _.sortBy(_.toPairs(_.countBy(samps)), '1');
-  return _.last(tallied)[0];
+  var last = _.last(tallied);
+  if (tallied.length > 1) {
+    var penultimate = tallied.slice(-2)[0];
+    if (penultimate[1] === last[1]) {
+      util.warn('Samples have more than one mode.');
+    }
+  }
+  return last[0];
 }
 
 // estimate the mode of a continuous distribution from some

tests/test-data/sampler/binomial.js

@@ -69,6 +69,12 @@ module.exports = {
     mode: function(params) {
       var p = params[0];
       var n = params[1];
+      // When (n+1)p is an integer and p != 0 or 1, then there are two
+      // modes: (n+1)p and (n+1)p - 1
+      if (Number.isInteger((n + 1) * p) &&
+          p !== 0 && p !== 1) {
+        throw new Error("Don't know how to test multimodal distributions.");
+      }
       return Math.floor((n + 1) * p)
     },
     variance: function(params) {

tests/test-samplers.js

@@ -58,10 +58,10 @@ var generateSettingTest = function(seed, distMetadata, settings) {
   var n = settings.n;
 
   // only test the stats that aren't blacklisted
-  var populationStatisticFunctions = _.pick(distMetadata.populationStatisticFunctions,
-                                            function(v, k) {
-                                              return !_.includes(settings.skip, k)
-                                            });
+  var populationStatisticFunctions = _.pickBy(distMetadata.populationStatisticFunctions,
+                                              function(v, k) {
+                                                return !_.includes(settings.skip, k)
+                                              });
   var group = {};
 
   var moment = distMetadata.moment;