HighCharts Trend Line Series Maker

highcharts-trend.js

/**
 * Originally this code was from:
 * https://github.com/virtualstaticvoid/highcharts_trendline
 *
 * But it dropped a lot in the global namespace, so I added a closure and exposed:
 *
 *     window.BuildHighChartsTrendLineSeriesFromSeries(series);
 *
 * If you want, I can make the name longer.
 * 
 * Here's how I use it:
 *
 *    $graph.highcharts({
 *      ...
 *      series: [
 *        window.BuildHighChartsTrendLineSeriesFromSeries(mySeries),
 *        mySeries
 *      ]
 *    });
 *
 */


/**
 * Code for regression extracted from jqplot.trendline.js
 *
 * Version: 1.0.0a_r701
 *
 * Copyright (c) 2009-2011 Chris Leonello
 * jqPlot is currently available for use in all personal or commercial projects
 * under both the MIT (http://www.opensource.org/licenses/mit-license.php) and GPL
 * version 2.0 (http://www.gnu.org/licenses/gpl-2.0.html) licenses. This means that you can
 * choose the license that best suits your project and use it accordingly.
 *
 **/

(function(){

  function regression(x, y, typ) {
    var type = (typ == null) ? 'linear' : typ;
    var N = x.length;
    var slope;
    var intercept;
    var SX = 0;
    var SY = 0;
    var SXX = 0;
    var SXY = 0;
    var SYY = 0;
    var Y = [];
    var X = [];

    if (type == 'linear') {
      X = x;
      Y = y;
    }
    else if (type == 'exp' || type == 'exponential') {
      for (var i = 0; i < y.length; i++) {
        // ignore points <= 0, log undefined.
        if (y[i] <= 0) {
          N--;
        }
        else {
          X.push(x[i]);
          Y.push(Math.log(y[i]));
        }
      }
    }

    for (var i = 0; i < N; i++) {
      SX = SX + X[i];
      SY = SY + Y[i];
      SXY = SXY + X[i] * Y[i];
      SXX = SXX + X[i] * X[i];
      SYY = SYY + Y[i] * Y[i];
    }

    slope = (N * SXY - SX * SY) / (N * SXX - SX * SX);
    intercept = (SY - slope * SX) / N;

    return [slope, intercept];
  }

  function linearRegression(X, Y) {
    var ret;
    ret = regression(X, Y, 'linear');
    return [ret[0], ret[1]];
  }

  function expRegression(X, Y) {
    var ret;
    var x = X;
    var y = Y;
    ret = regression(x, y, 'exp');
    var base = Math.exp(ret[0]);
    var coeff = Math.exp(ret[1]);
    return [base, coeff];
  }

  /*
   TODO: this function is quite inefficient.
   Refactor it if there is problem with speed.
   */
  function fitData(data, typ) {
    var type = (typ == null) ? 'linear' : typ;
    var ret;
    var res;
    var x = [];
    var y = [];
    var ypred = [];

    for (i = 0; i < data.length; i++) {
      if (data[i] != null && Object.prototype.toString.call(data[i]) === '[object Array]') {
        if (data[i] != null && data[i][0] != null && data[i][1] != null) {
          x.push(data[i][0]);
          y.push(data[i][1]);
        }
      }
      else if(data[i] != null && typeof data[i] === 'number' ){//If type of X axis is category
        x.push(i);
        y.push(data[i]);
      }
      else if(data[i] != null && Object.prototype.toString.call(data[i]) === '[object Object]'){
        if (data[i] != null && data[i].x != null && data[i].y != null) {
          x.push(data[i].x);
          y.push(data[i].y);
        }
      }
    }

    if (type == 'linear') {

      ret = linearRegression(x, y);
      for (var i = 0; i < x.length; i++) {
        res = ret[0] * x[i] + ret[1];
        ypred.push([x[i], res]);
      }

      return {
        data: ypred,
        slope: ret[0],
        intercept: ret[1],
        y: function(x) {
          return (this.slope * x) + this.intercept;
        },
        x: function(y) {
          return (y - this.intercept) / this.slope;
        }
      };
    }
    else if (type == 'exp' || type == 'exponential') {

      ret = expRegression(x, y);
      for (var i = 0; i < x.length; i++) {
        res = ret[1] * Math.pow(ret[0], x[i]);
        ypred.push([x[i], res]);
      }
      ypred.sort();

      return {
        data: ypred,
        base: ret[0],
        coeff: ret[1]
      };
    }
  }

  window.BuildHighChartsTrendLineSeriesFromSeries = function(series){
    return {
      type: 'line',
      marker: { enabled: false },
      data: fitData(series.data).data,
      enableMouseTracking: false,
      color: '#66ccff',
      dashStyle: 'ShortDash'
    };
  };

})();