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Run-length encoding: Difference between revisions
RLE decoder added
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(RLE decoder added) |
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=={{header|SQL}}==
{{works with|PL/pgSQL}}
<br>
* RLE encoding
<lang SQL>
Line 2,945 ⟶ 2,946:
where noWithinGroup = 1
) Rle_Compressed
</lang>
* RLE decoding
<lang SQL>
-- variable table
DROP TABLE IF EXISTS var;
CREATE temp TABLE var ( VALUE VARCHAR(1000) );
INSERT INTO var(VALUE) SELECT '1A2B3C4D5E6F';
-- select
WITH recursive
ints(num) AS
(
SELECT 1
UNION ALL
SELECT num+1
FROM ints
WHERE num+1 <= LENGTH((SELECT VALUE FROM var))
)
,
chars(num,chr,nextChr) AS
(
SELECT tmp.*
FROM (
SELECT num,
SUBSTRING((SELECT VALUE FROM var), num, 1) chr,
(SELECT SUBSTRING((SELECT VALUE FROM var), num+1, 1)) nextChr
FROM ints
) tmp
)
,
charsWithGroup(num,chr,nextChr,group_no) AS
(
SELECT *,(SELECT COUNT(*)
FROM chars chars2
WHERE chars2.chr !~ '[0-9]' AND
chars2.num < chars.num) group_No
FROM chars
)
,
charsWithGroupAndLetter(num,chr,nextChr,group_no,group_letter) AS
(
SELECT *,(SELECT chr
FROM charsWithGroup g2
where g2.group_no = charsWithGroup.group_no
ORDER BY num DESC
LIMIT 1)
FROM charsWithGroup
)
,
lettersWithCount(group_no,amount,group_letter) AS
(
SELECT group_no, string_agg(chr, '' ORDER BY num), group_letter
FROM charsWithGroupAndLetter
WHERE chr ~ '[0-9]'
GROUP BY group_no, group_letter
)
,
lettersReplicated(group_no,amount,group_letter, replicated_Letter) AS
(
SELECT *, rpad(group_letter, cast(amount as int), group_letter)
FROM lettersWithCount
)
select (SELECT value FROM var) rle_encoded,
string_agg(replicated_Letter, '' ORDER BY group_no) decoded_string
FROM lettersReplicated
</lang>
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