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Key: CORE-638
Type: New Feature New Feature
Status: Open Open
Priority: Major Major
Assignee: Unassigned
Reporter: Pavel Cisar
Votes: 4
Watchers: 2
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Firebird Core

Add statistical fucntions (as agreg.?)

Created: 17/Sep/03 12:00 AM   Updated: 31/Jan/14 09:33 AM
Component/s: UDF
Affects Version/s: None
Fix Version/s: None

SF_ID: 807974


 Description  « Hide
SFID: 807974#
Submitted By: pcisar

May be implemented in Firebird some statistical
functions?

- computing of Median
- computing of Standard deviation (StdDev)
- computing of Skew
- computing of Kurtosis
- common and central statistical moments

How can be computed:

Median - sort by values and get central value
PHP example:
    $this->int_get_sorted_data();
    $count = $this->data_count;
    $data = $this->data_sorted;
    if ($count % 2){
      $mediane = $data[($count - 1) / 2];
    } else {
      $mediane = ($data[$count/2] + $data[$count/2 -
1]) / 2;
    }

standard deviation =
= sqrt(1/(count(X) - 1) * sum(Xi - avg(x)))
= sqrt((sum(Xi^2) - (sum(Xi)^2)/(count(X) - 1))

Skew =
(count(X) * (sum((Xi - avg(X))^3))) /
((count(X)-1)*(count(X)-2)*stddev(X)^3))


Kurtosis
= (n*(n+1)*sum((Xi - avg(X))^4))/((n-1)*(n-2)*(n-3)
*stddev^4 - (3*(n-1)^2)/((n-2)*(n-3))
n = count(X)

Standard deviation, Kurtosis and Skew not teoretical
but selective (select).

r-th common moment:
MU'r(X) = avg(Xi^r)

r-th central moment:
MUr(X) = avg((Xi - avg(X))^r)

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Umberto Masotti added a comment - 20/Sep/06 02:03 AM
these functions are aggregates, and need a result set to give a singleton answer.

How can be passed a vector of results to a UDF?

Thay can be implemented simpler as internal function, as SUM(), COUNT(), AVG() are.

ramengo added a comment - 23/Sep/08 08:02 AM
When will be implemented these statistical functions ?
Is there any probability to see them in 2.5 ?

Dmitry Yemanov added a comment - 23/Sep/08 08:53 AM
Definitely, not in v2.5.

Dietrich Streifert added a comment - 07/Oct/09 12:07 AM
It would be definitely a benefit to have stddev and median as internal agregate functions.

Ivan added a comment - 24/Oct/09 07:38 PM
I think is be better if this support in UDF.

http://tracker.firebirdsql.org/browse/CORE-1326


Firebird User unter Windows7 added a comment - 31/Jan/14 09:33 AM
I would prefer a internal implementation in V3 like other databases does.