Add Standard Deviation calculation to smooth node

function/smooth/17-smooth.html

@@ -20,7 +20,8 @@
         <select id="node-input-action" style="width:60%; margin-right:5px;">
             <option value="max">Return the maximum value seen</option>
             <option value="min">Return the minimum value seen</option>
-            <option value="mean">Return the mean value seen</option>
+            <option value="mean">Return the mean value</option>
+            <option value="sd">Return the standard deviation</option>
             <option value="low">Perform low pass filter</option>
             <option value="high">Perform high pass filter</option>
         </select>

function/smooth/17-smooth.js

@@ -25,6 +25,7 @@ module.exports = function(RED) {
         var node = this;
         var a = [];
         var tot = 0;
+        var tot2 = 0;
         var pop = 0;
         var old = null;
 
@@ -51,6 +52,14 @@ module.exports = function(RED) {
                             tot = tot + n - pop;
                             msg.payload = tot / a.length;
                         }
+                        if (node.action === "sd") {
+                            tot = tot + n - pop;
+                            tot2 = tot2 + (n*n) - (pop * pop);
+                            if (a.length > 1) {
+                               msg.payload = Math.sqrt((a.length * tot2 - tot * tot)/(a.length * (a.length - 1)));
+                            }
+                            else { msg.payload = 0; }
+                        }
                     }
                     if (node.round) { msg.payload = Math.round(msg.payload); }
                     node.send(msg);

function/smooth/README.md

@@ -1,12 +1,21 @@
 node-red-node-smooth
 ====================
 
-A <a href="http://nodered.org" target="_new">Node-RED</a> node that provides several simple smoothing algorithms for incoming data values.
+A <a href="http://nodered.org" target="_new">Node-RED</a> node that provides
+several simple smoothing algorithms for incoming data values. These include
+
+ - Minimum
+ - Maximum
+ - Mean
+ - Standard Deviation
+ - High Pass Smoothing
+ - Loww Pass Smoothing
 
 Install
 -------
 
-Run the following command in the root directory of your Node-RED install
+Run the following command in the root directory of your Node-RED install. This
+is normally `~/.node-red`
 
     npm install node-red-node-smooth
 
@@ -14,11 +23,16 @@ Run the following command in the root directory of your Node-RED install
 Usage
 -----
 
-A simple node to provide various functions across several previous values, including max, min, mean, high and low pass filters.
+A simple node to provide various functions across several previous values,
+including max, min, mean, standard deviation, high and low pass filters.
 
-Max, Min and Mean work over a specified number of previous values.
+Max, Min, Mean and Standard Deviation work over a rolling window, based on a
+specified number of previous values.
 
-The High and Low pass filters use a smoothing factor. The higher the number the more the smoothing. E.g. a value of 10 is similar to an &alpha; of 0.1. It is analogous to an RC time constant - but there is no time component to this as the code is based on events arriving.
+The High and Low pass filters use a smoothing factor. The higher the number
+the more the smoothing. E.g. a value of 10 is similar to an &alpha; of 0.1.
+It is analogous to an RC time constant - but there is no time component to
+this as the code is based on events arriving.
 
-
-**Note:** This only operates on **numbers**. Anything else will try to be made into a number and rejected if that fails.
+**Note:** This node only operates on **numbers**. Anything else will try to be
+made into a number and rejected if that fails.

function/smooth/package.json

@@ -1,6 +1,6 @@
 {
     "name"          : "node-red-node-smooth",
-    "version"       : "0.0.4",
+    "version"       : "0.0.5",
     "description"   : "A Node-RED node that provides several simple smoothing algorithms for incoming data values.",
     "dependencies"  : {
     },
@@ -9,7 +9,7 @@
         "url":"https://github.com/node-red/node-red-nodes/tree/master/analysis/smooth"
     },
     "license": "Apache-2.0",
-    "keywords": [ "node-red", "smooth", "average" ],
+    "keywords": [ "node-red", "smooth", "average", "standard deviation" ],
     "node-red"      : {
         "nodes"     : {
             "smooth": "17-smooth.js"