added sum, mean, stdev computations and assertions

lib/calc.js

@@ -0,0 +1,55 @@
+/*!
+ * Chai Stats - calculation utilities
+ * Copyright (c) 2012 Jake Luer <jake@alogicalparadox.com>
+ * MIT Licenced
+ */
+
+/**
+ * # sum
+ *
+ * Returns the sum of a given array of numbers.
+ *
+ * @param {Array} numbers to sum
+ * @returns sum
+ */
+
+exports.sum = function (nums) {
+  var res = 0;
+  for (var i = 0; i < nums.length; i++)
+    res += nums[i];
+  return res;
+};
+
+/**
+ * # mean
+ *
+ * Returns the mean (average) of a given array of numbers.
+ *
+ * @param {Array} numbers to average
+ * @returs mean
+ */
+
+exports.mean = function (nums) {
+  var sum = exports.sum(nums);
+  return sum / nums.length;
+};
+
+/**
+ * # sdeviation
+ *
+ * Returns the standard deviation of a given array of numbers.
+ *
+ * @param {Array} numbers for stdev
+ * @return standard deviation
+ */
+
+exports.sdeviation = function (nums) {
+  var devs = []
+    , mean = exports.mean(nums);
+  for (var i = 0; i < nums.length; i++)
+    devs.push(nums[i] - mean);
+  for (var d = 0; d < devs.length; d++)
+    devs[d] = Math.pow(devs[d], 2);
+  var davg = exports.sum(devs) / (devs.length - 1);
+  return Math.sqrt(davg);
+};

lib/stats.js

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+var calc = require('./calc');
+
+module.exports = function (chai, _) {
+
+  _.addProperty(chai.Assertion, 'sum', function () {
+    var obj = _.flag(this, 'object');
+    new chai.Assertion(obj).to.be.instanceOf(Array);
+    _.flag(this, 'object', calc.sum(obj));
+  });
+
+  _.addProperty(chai.Assertion, 'mean', function () {
+    var obj = _.flag(this, 'object');
+    new chai.Assertion(obj).to.be.instanceOf(Array);
+    _.flag(this, 'object', calc.mean(obj));
+  });
+
+  function deviation () {
+    var obj = _.flag(this, 'object');
+    new chai.Assertion(obj).to.be.instanceOf(Array);
+    _.flag(this, 'object', calc.sdeviation(obj));
+  }
+
+  _.addProperty(chai.Assertion, 'stdev', deviation);
+  _.addProperty(chai.Assertion, 'deviation', deviation);
+
+};