MEDIAN as custom aggregate?

Folks,

Hey, anybody have a custom aggregate for median calucation? I'm doing
this through a PL/pgSQL function, and a custom aggregate would probably
be faster.

For those whose stats terminology is rusty, the "median" is the "middle"
value in a distribution. For example, if we had the following data:

Table ages
person age
Jim 21
Rusty 24
Carol 37
Bob 62
Leah 78

Our Median would be Carol's age, 37. This is a different figure from
the Mean, or Average, which is 44.4. Using the combination of the Mean
and the Median you can do all kinds of interesting statistical analysis.

-Josh Berkus

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