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Make sure that empty arrays or arrays with all the same entry return 0 for Skewness and Kurtosis rather than throwing a division by zero error

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This commit is contained in:
Stuart Lynn 2015-12-04 14:54:15 -05:00
parent a88bfc51a3
commit 0ecbbd8e71
1 changed files with 22 additions and 16 deletions
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38
scripts-available/CDB_Stats.sql
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@ -4,7 +4,7 @@
-- @param in_array A numeric array of numbers
--
-- Returns: statistical quantity chosen
--
--
-- References: http://www.itl.nist.gov/div898/handbook/eda/section3/eda35b.htm
--
@ -13,17 +13,21 @@ CREATE OR REPLACE FUNCTION CDB_Kurtosis ( in_array NUMERIC[] ) RETURNS NUMERIC a
DECLARE
a numeric;
c numeric;
s numeric;
k numeric;
BEGIN
SELECT AVG(e), COUNT(e)::numeric, stddev(e) INTO a, c, s FROM ( SELECT unnest(in_array) e ) x;
SELECT AVG(e), COUNT(e)::numeric * power(stddev(e),4) INTO a, c FROM ( SELECT unnest(in_array) e ) x;
EXECUTE 'SELECT sum(power($1 - e, 4)) / ( $2 * power($3, 4)) - 3
FROM (SELECT unnest($4) e ) x'
INTO k
USING a, c, s, in_array;
IF c=0 THEN
RETURN 0;
ELSE
RETURN k;
EXECUTE 'SELECT sum(power($1 - e, 4)) / ($2 ) - 3
FROM (SELECT unnest($3) e ) x'
INTO k
USING a, c, in_array;
RETURN k;
END IF;
END;
$$ language plpgsql IMMUTABLE;
@ -32,16 +36,18 @@ CREATE OR REPLACE FUNCTION CDB_Skewness ( in_array NUMERIC[] ) RETURNS NUMERIC a
DECLARE
a numeric;
c numeric;
s numeric;
sk numeric;
BEGIN
SELECT AVG(e), COUNT(e)::numeric, stddev(e) INTO a, c, s FROM ( SELECT unnest(in_array) e ) x;
SELECT AVG(e), COUNT(e)::numeric * power(stddev(e),3) INTO a, c FROM ( SELECT unnest(in_array) e ) x;
IF c=0 THEN
RETURN 0;
ELSE
EXECUTE 'SELECT sum(power($1 - e, 3)) / ( $2 )
FROM (SELECT unnest($3) e ) x'
INTO sk
USING a, c, in_array;
EXECUTE 'SELECT sum(power($1 - e, 3)) / ( $2 * power($3, 3))
FROM (SELECT unnest($4) e ) x'
INTO sk
USING a, c, s, in_array;
RETURN sk;
RETURN sk;
END IF;
END;
$$ language plpgsql IMMUTABLE;