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47 lines
1.4 KiB
47 lines
1.4 KiB
--
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-- Determine the Heads/Tails classifications from a numeric array
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--
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-- @param in_array A numeric array of numbers to determine the best
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-- bins based on the Heads/Tails method.
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--
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-- @param breaks The number of bins you want to find.
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--
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--
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CREATE OR REPLACE FUNCTION @extschema@.CDB_HeadsTailsBins ( in_array NUMERIC[], breaks INT) RETURNS NUMERIC[] as $$
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DECLARE
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element_count INT4;
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arr_mean numeric;
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i INT := 2;
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reply numeric[];
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BEGIN
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-- get the total size of our row
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element_count := array_upper(in_array, 1) - array_lower(in_array, 1);
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-- ensure the ordering of in_array
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SELECT array_agg(e) INTO in_array FROM (SELECT unnest(in_array) e ORDER BY e) x;
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-- stop if no rows
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IF element_count IS NULL THEN
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RETURN NULL;
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END IF;
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-- stop if our breaks are more than our input array size
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IF element_count < breaks THEN
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RETURN in_array;
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END IF;
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-- get our mean value
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SELECT avg(v) INTO arr_mean FROM ( SELECT unnest(in_array) as v ) x;
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reply = Array[arr_mean];
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-- slice our bread
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LOOP
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IF i > breaks THEN EXIT; END IF;
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SELECT avg(e) INTO arr_mean FROM ( SELECT unnest(in_array) e) x WHERE e > reply[i-1];
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IF arr_mean IS NOT NULL THEN
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reply = array_append(reply, arr_mean);
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END IF;
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i := i+1;
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END LOOP;
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RETURN reply;
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END;
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$$ language plpgsql IMMUTABLE PARALLEL SAFE;
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