Rolling median algorithm in C

Question

I am currently working on an algorithm to implement a rolling median filter (analogous to a rolling mean filter) in C. From my search of the literature, there appear to be t

Answer 1

Here is one that can be used when exact output is not important (for display purposes etc.) You need totalcount and lastmedian, plus the newvalue.

{
totalcount++;
newmedian=lastmedian+(newvalue>lastmedian?1:-1)*(lastmedian==0?newvalue: lastmedian/totalcount*2);
}

Produces quite exact results for things like page_display_time.

Rules: the input stream needs to be smooth on the order of page display time, big in count (>30 etc), and have a non zero median.

Example: page load time, 800 items, 10ms...3000ms, average 90ms, real median:11ms

After 30 inputs, medians error is generally <=20% (9ms..12ms), and gets less and less. After 800 inputs, the error is +-2%.

Another thinker with a similar solution is here: Median Filter Super efficient implementation