JavaScript Array Math Utils: Math.log Math.logArray Math.expArray Math.diffArray Math.roundArray Array.prototype.transpose addArray pastorFuture. Use these together for forecasting functions. Example: Math.roundArray(Math.diffArray(Math.logArray([10, 100, 1000, 10000])), 3);

array.math.js

/*  JAVASCRIPT ARRAY MATH UTILS
    Use these together for forecasting functions  
    Example: Math.roundArray(Math.diffArray(Math.logArray([10, 100, 1000, 10000])), 3);

    Math.log
    
    Math.logArray
    Math.expArray
    Math.diffArray
    Math.roundArray
    
    Array.prototype.transpose
    addArray
    pastorFuture
*/

//  ARRAY MATH


//  Math.log(number, base), e.g. Math.log(10, 2)

Math.log = (function() {
    var log = Math.log;
    return function(n, base) {
        return log(n)/(base ? log(base) : 1);
    };
})();

// Math.logArray([array], optional_base)
// Assumes natural log if base is omitted. Returns an array of logarithms 
// Example: Math.logArray([5, 2], 10); Math.logArray([20, 7, Math.E]);

Math.logArray = (function() {
    return function(input_array, base) {
    
    var output_array = [];
    if (input_array instanceof Array) {
    	for (var i = 0; i < input_array.length; i++) {
    		output_array.push(Math.log(input_array[i], base));
    	}
    	return output_array;
    }
    else
    	return null;
  };
})();

// Math.expArray(array), e.g. Math.expArray([5, 2]);

Math.expArray = (function() {
    return function(input_array) {
    
    var output_array = [];
    if (input_array instanceof Array) {
    	for (var i = 0; i < input_array.length; i++) {
    		output_array.push(Math.exp(input_array[i]));
    	}
    	return output_array;
    }
    else
    	return null;
  };
})();

// Math.diffArray([array])
// Returns an array of differences between array elements.  First element returned is NaN, null evaluates to 0
// Example: Math.diffArray([5, 2]);

Math.diffArray = (function() {
    return function(input_array) {
    
    var output_array = [];
    if (input_array instanceof Array) {
    	for (var i = 0; i < input_array.length; i++) {
    		output_array.push(input_array[i] - input_array[i-1]);
    	}
    	return output_array;
    }
    else
    	return null;
  };
})();

// Math.roundArray([array], optional_decimal_places)
// Assumes 0 decimal places as the default
// Example: Math.roundArray([5.2222, 2.5555], 3);

// Will not work for ([1.005],2) which comes out as [1] instead of [1.01], 
// see: http://stackoverflow.com/questions/11832914/round-up-to-2-decimal-places-in-javascript#comment26122771_11832950

Math.roundArray = (function() {
    return function(input_array, decimals) {
    
    var output_array = [];
    if (!decimals)
        decimals = 0;
        
    if (input_array instanceof Array) {
    	for (var i = 0; i < input_array.length; i++) {
    		output_array.push(Math.round(input_array[i] * Math.pow(10,decimals)) / Math.pow(10,decimals));
    	}
    	return output_array;
    }
    else
    	return null;
  };
})();

//  ARRAY TRANSFORMATIONS


// http://stackoverflow.com/questions/4492678/to-swap-rows-with-columns-of-matrix-in-javascript-or-jquery
Array.prototype.transpose = function() {

  // Calculate the width and height of the Array
  var a = this,
    w = a.length ? a.length : 0,
    h = a[0] instanceof Array ? a[0].length : 0;

  // In case it is a zero matrix, no transpose routine needed.
  if(h === 0 || w === 0) { return []; }

  /**
   * @var {Number} i Counter
   * @var {Number} j Counter
   * @var {Array} t Transposed data is stored in this array.
   */
  var i, j, t = [];

  // Loop through every item in the outer array (height)
  for(i=0; i<h; i++) {

    // Insert a new row (array)
    t[i] = [];

    // Loop through every item per item in outer array (width)
    for(j=0; j<w; j++) {

      // Save transposed data.
      t[i][j] = a[j][i];
    }
  }

  return t;
};

// assume both arrays are sorted by first column
// second array must have exactly 2 columns
// first array must include all years
// a = [[2007,2], [2008, 4]];
// b = [[2008, 18],[2009, 4], [2010, 8]];

function addArray (output_array, second_array) {
    if (second_array.length > 0 && second_array[0].length == 2) {        

        // iterate through each row of output_array
        for (var i = 0; i < output_array.length; i++) {
            var j = 0;
            while ((j < second_array.length) && (output_array[i][0] > second_array[j][0]))
            	j++;
            if ((j < second_array.length) && (output_array[i][0] == second_array[j][0]))
                output_array[i].push(second_array[j][1]);
            else
                output_array[i].push(null);  
        }
    }
    return output_array;
}

// assume array is sorted by first column
// assume array has exactly 2 columns
// a = [[2008, 18],[2009, 4], [2010, 8], [2012, 8], [2013, 8], [2014, 8]];

function pastorFuture(array) {
    var array_length = array.length;
    // if (array_length)
    //     var array_width = array[0].length;
    var year = new Date().getFullYear();
    if (array_length && array[0][0] <= year && array[array_length-1][0] > year) {
        for (var i = 0; i < array_length; i++) {
                if (array[i][0] < year)
                    array[i].push(null);
                else if (array[i][0] == year)
                    array[i].push(array[i][1]);
                else
                    array[i] = [array[i][0],null,array[i][1]];                
        }
    }
    return array;
}