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RE: vector-last / vector-ref with negative indices?

From: dsmich
Subject: RE: vector-last / vector-ref with negative indices?
Date: Sun, 20 Dec 2020 13:44:18 +0000

Maybe sort the vector in the other direction and access with index 0


        -----------------------------------------From: "Aleix Conchillo
To: "guile-user"
Sent: Sunday December 20 2020 1:59:04AM
Subject: vector-last / vector-ref with negative indices?


 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
 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
 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,


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