Re: How to delete few elements from array beginning?

[Chris Travers <chris.travers@xxxxxxxxx>]

On Wed, Mar 9, 2016 at 4:53 PM, Alexander Farber <alexander.farber@xxxxxxxxx> wrote:

Hello Chris,

On Wed, Mar 9, 2016 at 4:42 PM, Chris Travers <chris.travers@xxxxxxxxx> wrote:

On Wed, Mar 9, 2016 at 1:10 PM, Alexander Farber <alexander.farber@xxxxxxxxx> wrote:

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.

actually card hands would be easier - because cards are unique in the deck.

But here I have letter hands (like "AAABCDE") in a word game and they are not unique in the pile...

But it seems like a similar problem.  Namely:

1.  You have an ordered list of cards (these may be lettered cards).  These start out as existing in a shuffled deck but once shuffled you have an order.  Whether or not the cards are unque

2.  When you draw a card, you have to remove it from the head of the list.

Now on to some basic points (though you can probably do this in a straight SQL query):

SQL arrays are more or less like math matrices.  For this reason it doesn't make sense to treat them as programming structures per se.  Instead you have a matrix and you create another matrix by slicing it. So this is how you have to think about the problem.

Also consider that PostgreSQL tuples are copy on write anyway.

Now, if you want something that uses an array more like a queue, it is best to write that portion in pl/perl.  However if you do that you have to think carefully about mutability.

Hope this helps

Chris Travers

Regards

Alex

--

Best Wishes,

Chris Travers

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