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From: Christopher Lam <christopher.lck@gmail.com>
To: "Aleix Conchillo Flaqué" <aconchillo@gmail.com>
Cc: guile-user <guile-user@gnu.org>
Subject: Re: vector-last / vector-ref with negative indices?
Date: Sun, 20 Dec 2020 10:05:51 +0000	[thread overview]
Message-ID: <CAKVAZZKc55X+H0FVqmPnexMSAvFsYLeSgYwA5QZ997BSwkkNkA@mail.gmail.com> (raw)
In-Reply-To: <CA+XASoWHOs6+EfaD22+yu44-ObJEJkzsajC49A8Ce8RtjNkC4Q@mail.gmail.com>

Easy - vector-ref with a negative index is not defined in r[5|7]rs.

On Sun, 20 Dec 2020 at 06:59, Aleix Conchillo Flaqué <aconchillo@gmail.com>
wrote:

> Hi,
>
> This month I'm trying to go through Advent Of Code one more year
> (previous years I didn't get too far) and I've been finding myself
> writing the same patterns multiple times that could be avoided by just
> having a helper function.
>
> One of them is getting the last element of a vector. It is a quite
> common operation when solving these types of problems. For example
> Python as you might know uses negative indices.
>
> I have looked around and haven't seen it (unless I completely missed
> it which would be shameful) but wouldn't it be good to have this
> built-in by default?
>
> Instead of having to write:
>
> (vector-ref v (- (vector-length v) 1))
>
> you would write:
>
> (vector-last v) or even better (vector-ref v -1).
>
> Interestingly Racket doesn't offer those functions either as far as I can
> tell.
>
> Basic use case? Get the maximum element of a sorted vector which would
> be done in constant time.
>
> I'm trying to solve the problems idiomatically, to the best of my
> limited knowledge, with Scheme. It is possible that the times I'm
> using vectors I should think about it differently and not use them,
> but I'm not 100% sure.
>
> What am I missing?
>
> Thank you in advance,
>
> Aleix
>
>


  reply	other threads:[~2020-12-20 10:05 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-20  6:58 vector-last / vector-ref with negative indices? Aleix Conchillo Flaqué
2020-12-20 10:05 ` Christopher Lam [this message]
2020-12-20 10:41   ` lloda
2020-12-21  9:50 ` Aleix Conchillo Flaqué
  -- strict thread matches above, loose matches on Subject: below --
2020-12-20 13:44 dsmich

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