CODEWITHSUNDEEP
postgresql
PostGreSQL newbie
PostGreSQL newbie

Reputation: 21

PotgreSQL 2D array to rows

I am new to PostgreSQL array's.

I am trying to a write a procedure to convert array-into-rows, and wanted following output:

alphabet | number
---------+----------
       A |      10
       B |      10
       C |       6
       D |       9
       E |       3



from following:


id |                                     alphabet_series                                                                                
-------+--------------------------------------------------------------------------------------------------
     1 | {{A,10},{B,10},{C,6},{D,9},{E,3},{F,9},{I,10},{J,17},{K,16},{L,17},{M,20},{N,13},{O,19}}

I have searched for array-to-rows functions, but they all seems to accept 1-d array. but in this case, it is 2-d array.

Any pointers will be appreciated.

Many thanks.

Upvotes: 2

Views: 2303

Answers (3)

poshest
poshest

Reputation: 4237

CREATE OR REPLACE FUNCTION unnest_2d(anyarray)
  RETURNS table(col1 text, col2 text)  AS
$BODY$
DECLARE
  _col1 text[];
  _col2 text[];
BEGIN
  _col1 := $1[1:array_length($1, 1)][1:1];
  _col2 := $1[1:array_length($1, 1)][2:2];
  return query (SELECT * FROM unnest(_col1,_col2));
END
$BODY$  LANGUAGE plpgsql IMMUTABLE;

SELECT * FROM unnest_2d('{{A,a},{B,b}}'::text[][]);

Upvotes: 1

Konrad Garus
Konrad Garus

Reputation: 54005

CREATE TABLE two_d (x text, y text);

CREATE OR REPLACE FUNCTION unnest_2d(anyarray)
  RETURNS SETOF two_d AS
$BODY$
  SELECT $1[i][1], $1[i][2] FROM
   generate_series(array_lower($1,1),
                    array_upper($1,1)) i
$BODY$
  LANGUAGE 'sql' IMMUTABLE;

SELECT * FROM unnest_2d('{{A,a},{B,b}}'::text[][]);

Upvotes: 2

Peter Tillemans
Peter Tillemans

Reputation: 35331

I would create a table with 3 fields :

CREATE TABLE matrix ( ROW CHAR, COL INT, VALUE )

and fill it with your matrix then you can query it using :

SELECT ROW, SUM(VALUE) FROM matrix GROUP BY COLUMN ORDER BY ROW;

or similar.

This will work fine if the matrix is of a reasonable size (like not billions of elements)

Upvotes: 0

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