Re: How to delete few elements from array beginning?

On Wed, Mar 9, 2016 at 1:10 PM, Alexander Farber <alexander(dot)farber(at)gmail(dot)com
> wrote:

> Hello fellow PostgreSQL users,
>
> what is please the most efficient way to delete a slice from the start of
> a longer array (after I have copied it to another array)?
>
> Do I really have to copy a large slice of the array to itself, like in the
> last line here:
>
> pile_array := pile_array || swap_array;
>
> /* here I copy away swap_len elements */
> new_hand := pile_array[1:swap_len];
>
> /* here I don't know how to efficiently remove already copied
> elements */
> pile_array := pile_array[(swap_len + 1):ARRAY_LENGTH(pile_array,
> 1)];
>
> or is there a better way?
>

This looks like something for card hands?

What you are doing seems correct to me.

>
> Thank you
> Alex
>
> P.S. The listing of the entire stored function in question:
>
> CREATE OR REPLACE FUNCTION words_swap_game(
> IN in_uid integer,
> IN in_gid integer,
> IN in_swap varchar(7))
> RETURNS void AS
> $func$
> DECLARE
> i integer;
> j integer;
> swap_len integer;
> hand_len integer;
> pile_len integer;
> swap_array varchar[];
> pile_array varchar[];
> old_hand varchar[];
> new_hand varchar[];
> hand_ignore boolean[];
> BEGIN
> swap_array := STRING_TO_ARRAY(in_swap, NULL);
> swap_len := ARRAY_LENGTH(swap_array, 1);
>
> SELECT hand1, pile, ARRAY_LENGTH(hand1, 1), ARRAY_LENGTH(pile, 1)
> INTO old_hand, pile_array, hand_len, pile_len
> FROM words_games
> WHERE gid = in_gid
> AND player1 = in_uid
> /* and it is first player's turn */
> AND (played1 IS NULL OR played1 < played2);
>
> IF NOT FOUND THEN
> SELECT hand2, pile, ARRAY_LENGTH(hand2, 1),
> ARRAY_LENGTH(pile, 1)
> INTO old_hand, pile_array, hand_len, pile_len
> FROM words_games
> WHERE gid = in_gid
> AND player2 = in_uid
> /* and it is second player's turn */
> AND (played2 IS NULL OR played2 < played1);
> END IF;
>
> pile_array := pile_array || swap_array;
> -- pile_array := words_shuffle(pile_array);
> new_hand := pile_array[1:swap_len];
> pile_array := pile_array[(swap_len + 1):pile_len]; /* XXX is it
> good? */
>
> hand_ignore := ARRAY_FILL(FALSE, ARRAY[hand_len]);
>
> <<hand_loop>>
> FOR i IN 1..hand_len LOOP
> FOR j IN 1..swap_len LOOP
> IF hand_ignore[j] = FALSE AND
> old_hand[i] = swap_array[j] THEN
> hand_ignore[j] := TRUE;
> CONTINUE hand_loop;
> END IF;
> END LOOP;
>
> new_hand := new_hand || old_hand[i];
> END LOOP;
> /*
> UPDATE words_games
> SET hand1 = new_hand,
> pile = pile_array,
> played1 = CURRENT_TIMESTAMP
> WHERE gid = in_gid
> AND player1 = in_uid
> -- and it is first player's turn
> AND (played1 IS NULL OR played1 < played2);
>
> IF NOT FOUND THEN
> UPDATE words_games
> SET hand2 = new_hand,
> pile = pile_array,
> played2 = CURRENT_TIMESTAMP
> WHERE gid = in_gid
> AND player2 = in_uid
> -- and it is second player's turn
> AND (played2 IS NULL OR played2 < played1);
> END IF;
> */
>
> END
> $func$ LANGUAGE plpgsql;
>
>
>
>

--
Best Wishes,
Chris Travers

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