webppl/src/dists/sampleBasedMarginal.js

Probabilistic programming for the web

'use strict';
var ad = require('../ad');
var _ = require('lodash');
var base = require('./base');
var util = require('../util');
var marginal = require('./marginal');
var SampleBasedMarginal = base.makeDistributionType({
    name: 'SampleBasedMarginal',
    nodoc: true,
    nohelper: true,
    params: [{ name: 'samples' }],
    mixins: [base.finiteSupport],
    constructor: function () {
        if (!_.isArray(this.params.samples) || this.params.samples.length === 0) {
            throw new Error('Expected samples to be a non-empty array.');
        }
        this.samples = this.params.samples;
        this.getDist = function () {
            if (this._cacheddist) {
                return this._cacheddist;
            } else {
                var dist = {};
                this.params.samples.forEach(function (obj) {
                    var val = obj.value;
                    var key = util.serialize(val);
                    if (dist[key] === undefined) {
                        dist[key] = {
                            val: val,
                            prob: 0
                        };
                    }
                    dist[key].prob += 1;
                });
                var n = this.params.samples.length;
                _.each(dist, function (obj) {
                    obj.prob /= n;
                });
                this._cacheddist = dist;
                return dist;
            }
        };
    },
    sample: function () {
        var n = this.params.samples.length;
        return this.params.samples[Math.floor(util.random() * n)].value;
    },
    score: function (val) {
        var key = util.serialize(val);
        var obj = this.getDist()[key];
        return obj === undefined ? -Infinity : Math.log(obj.prob);
    },
    support: function () {
        if (this.params.samples.length === 1) {
            return [this.params.samples[0].value];
        } else if (this._cachedsupport) {
            return this._cachedsupport;
        } else {
            var support = _.map(this.getDist(), _.property('val'));
            this._cachedsupport = support;
            return support;
        }
    },
    print: function () {
        return marginal.print(this.getDist());
    }
});
module.exports = { SampleBasedMarginal: SampleBasedMarginal };