runningavg.html

---
title: runningavg
brief: Keep a running calculation of the average value of a series
updated: 2014-08-14 13:12
layout: script

return: the new average value
---

<strong>Keys: 2</strong>
<ul class="args">
  <li>1: Key to store the current average.</li>
  <li>2: Key to store the current count of values.</li>
</ul>

<strong>Args: 1</strong>
<ul class="args">
  <li>the next value in the series</li>
</ul>

<h2>Description</h2>

This script can be used to keep a running average of a series of values, without
needing to keep each of the individual values around.

<h2>Example</h2>

<pre class="script-example">
> evalsha 399fddde578fd9cb924edce746c783e8340d8251 2 score:avg score:count 80
"80"
> evalsha 399fddde578fd9cb924edce746c783e8340d8251 2 score:avg score:count 100
"90"
> evalsha 399fddde578fd9cb924edce746c783e8340d8251 2 score:avg score:count 75
"85"
> evalsha 399fddde578fd9cb924edce746c783e8340d8251 2 score:avg score:count 98
"88.25"
> evalsha 399fddde578fd9cb924edce746c783e8340d8251 2 score:avg score:count 98
"90.2"
> evalsha 399fddde578fd9cb924edce746c783e8340d8251 2 score:avg score:count 98
"91.5"
> get score:avg
"91.5"
> get score:count
"6"
</pre>


<h2>Source</h2>

<pre class="script-source">
local currentval = tonumber(redis.call('get', KEYS[1])) or 0
local count = redis.call('incr', KEYS[2])

currentval = tostring(currentval * (count - 1)/count + (ARGV[1]/count))

redis.call('set', KEYS[1], currentval)
return currentval
</pre>