Merge pull request #125 from llimllib/master

Fix ckmeans
simple-statistics · Aug 17, 2015 · b938e56 · b938e56
2 parents 519799b + 95abb23
commit b938e56
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Showing 2 changed files with 9 additions and 7 deletions.
diff --git a/src/ckmeans.js b/src/ckmeans.js
@@ -106,14 +106,14 @@ function ckmeans(data, nClusters) {
                 var squaredDifference = Math.pow(
                     sorted[sortedIdx] - firstClusterMean, 2);
                 matrix[cluster][sortedIdx] = matrix[cluster][sortedIdx - 1] +
-                    ((sortedIdx - 1) / sortedIdx) * squaredDifference;
+                    (sortedIdx / (sortedIdx + 1)) * squaredDifference;
 
                 // We're computing a running mean by taking the previous
                 // mean value, multiplying it by the number of elements
                 // seen so far, and then dividing it by the number of
                 // elements total.
                 var newSum = sortedIdx * firstClusterMean + sorted[sortedIdx];
-                firstClusterMean = newSum / sortedIdx;
+                firstClusterMean = newSum / (sortedIdx + 1);
 
             } else {
 

diff --git a/test/ckmeans.test.js b/test/ckmeans.test.js
@@ -21,11 +21,13 @@ test('C k-means', function(t) {
     t.deepEqual(example, [[-1, -1, -1, -1], [2, 2, 2], [4, 5, 6]]);
     t.deepEqual(cK([1, 2, 3], 3), [[1], [2], [3]]);
 
-    // is this right?
-    t.deepEqual(cK([1, 2, 2, 3], 3), [[1, 2], [2], [3]]);
-    t.deepEqual(cK([1, 2, 2, 3, 3], 3), [[1, 2], [2], [3, 3]]);
-    t.deepEqual(cK([1, 2, 3, 2, 3], 3), [[1, 2], [2], [3, 3]]);
-    t.deepEqual(cK([3, 2, 3, 2, 1], 3), [[1, 2], [2], [3, 3]]);
+    t.deepEqual(cK([0, 3, 4], 2), [[0], [3, 4]]),
+    t.deepEqual(cK([-3, 0, 4], 2), [[-3, 0], [4]]),
+
+    t.deepEqual(cK([1, 2, 2, 3], 3), [[1], [2, 2], [3]]);
+    t.deepEqual(cK([1, 2, 2, 3, 3], 3), [[1], [2, 2], [3, 3]]);
+    t.deepEqual(cK([1, 2, 3, 2, 3], 3), [[1], [2, 2], [3, 3]]);
+    t.deepEqual(cK([3, 2, 3, 2, 1], 3), [[1], [2, 2], [3, 3]]);
     t.deepEqual(cK([3, 2, 3, 5, 2, 1], 3), [[1, 2, 2], [3, 3], [5]]);
 
     t.deepEqual(cK([0, 1, 2, 100, 101, 103], 2), [[0, 1, 2], [100, 101, 103]]);