47 lines
1.4 KiB
PL/PgSQL
47 lines
1.4 KiB
PL/PgSQL
--
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-- CDB_DistinctMeasure
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-- calculates the fraction of rows in the 10 most common distinct categories
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-- returns true if the number of rows in these 10 categories is >= 0.9 * total number of rows
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--
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--
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CREATE OR REPLACE FUNCTION CDB_DistinctMeasure ( in_array text[], threshold numeric DEFAULT 0.90 ) RETURNS boolean as $$
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DECLARE
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element_count INT4;
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maxval numeric;
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passes boolean;
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BEGIN
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SELECT count(e) INTO element_count FROM ( SELECT unnest(in_array) e ) x;
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-- count number of occurrences per bin
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-- calculate the normalized cumulative sum
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-- return the max value: which corresponds nth entry
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-- for n <= 10 depending on # of distinct values
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EXECUTE 'WITH a As (
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SELECT
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count(*) cnt,
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e
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FROM
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(SELECT * FROM unnest($2) e ) x
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GROUP BY e
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ORDER BY cnt DESC
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),
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b As (
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SELECT
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sum(cnt) OVER (ORDER BY cnt DESC) / $1 As cumsum
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FROM a
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LIMIT 10
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)
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SELECT max(cumsum) maxval FROM b'
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INTO maxval
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USING element_count, in_array;
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passes = CASE WHEN maxval >= threshold
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THEN TRUE
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ELSE FALSE
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END;
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RAISE NOTICE 'maxval: %', maxval;
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RETURN passes;
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END;
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$$ language plpgsql IMMUTABLE;
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