Array.avg Array.stdDev

2 files changed, 25 insertions, 0 deletions

diff --git a/jstests/array3.js b/jstests/array3.js
new file mode 100644
index 00000000000..3d053f99417
--- /dev/null
+++ b/jstests/array3.js
@@ -0,0 +1,8 @@
+
+assert.eq( 5 , Array.sum( [ 1 , 4 ] ), "A" )
+assert.eq( 2.5 , Array.avg( [ 1 , 4 ] ), "B" )
+
+arr = [ 2 , 4 , 4 , 4 , 5 , 5 , 7 , 9 ]
+assert.eq( 5 , Array.avg( arr ) , "C" )
+assert.eq( 2 , Array.stdDev( arr ) , "D" )
+
diff --git a/shell/utils.js b/shell/utils.js
index e7a45fe4b2b..37f512b7ea7 100644
--- a/shell/utils.js
+++ b/shell/utils.js
@@ -255,6 +255,23 @@ Array.sum = function( arr ){
     return s;
 }
 
+Array.avg = function( arr ){
+    if ( arr.length == 0 )
+        return null;
+    return Array.sum( arr ) / arr.length;
+}
+
+Array.stdDev = function( arr ){
+    var avg = Array.avg( arr );
+    var sum = 0;
+
+    for ( var i=0; i<arr.length; i++ ){
+        sum += Math.pow( arr[i] - avg , 2 );
+    }
+
+    return Math.sqrt( sum / arr.length );
+}
+
 if ( ! ObjectId.prototype )
     ObjectId.prototype = {}