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Cristina Ghirlanda  
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 More options Dec 27 2002, 2:28 pm
Newsgroups: comp.lang.lisp
From: Cristina Ghirlanda <cri...@NOSPAM.interfree-DOT-it>
Date: 27 Dec 2002 20:31:52 +0100
Local: Fri, Dec 27 2002 2:31 pm
Subject: remove the first element from a vector
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Hi,

  I wrote a function that removes the first element from a vector, but
  I think it's not the typical way people write in lisp.

(defun remove-first-from-vector (vector)
  (let (new-vector)
    (do ((index (1- (array-dimension vector 0)) (1- index)))
        ((= index 0) (concatenate 'vector new-vector))
      (push (aref vector index) new-vector))))  

  I would like to hear some advice on how I can write it in a
  more lispy way. Thanks.

Cristina


 
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Peter Seibel  
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 More options Dec 27 2002, 2:47 pm
Newsgroups: comp.lang.lisp
From: Peter Seibel <pe...@javamonkey.com>
Date: Fri, 27 Dec 2002 19:46:57 GMT
Local: Fri, Dec 27 2002 2:46 pm
Subject: Re: remove the first element from a vector
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Cristina Ghirlanda <cri...@NOSPAM.interfree-DOT-it> writes:
> Hi,

>   I wrote a function that removes the first element from a vector, but
>   I think it's not the typical way people write in lisp.

> (defun remove-first-from-vector (vector)
>   (let (new-vector)
>     (do ((index (1- (array-dimension vector 0)) (1- index)))
>         ((= index 0) (concatenate 'vector new-vector))
>       (push (aref vector index) new-vector))))  

>   I would like to hear some advice on how I can write it in a
>   more lispy way. Thanks.

I'm no expert but it seems like you can just do:

  (defun remove-first-from-vector (vector)
    (subseq vector 1))

-Peter

--
Peter Seibel
pe...@javamonkey.com


 
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Cristina Ghirlanda  
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 More options Dec 27 2002, 2:55 pm
Newsgroups: comp.lang.lisp
From: Cristina Ghirlanda <cri...@NOSPAM.interfree-DOT-it>
Date: 27 Dec 2002 20:58:41 +0100
Local: Fri, Dec 27 2002 2:58 pm
Subject: Re: remove the first element from a vector
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> I'm no expert but it seems like you can just do:
>   (defun remove-first-from-vector (vector)
>     (subseq vector 1))
> -Peter

Thanks, I didn't remember at all that vector is a sequence.

Cristina


 
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Barry Margolin  
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 More options Dec 27 2002, 3:02 pm
Newsgroups: comp.lang.lisp
From: Barry Margolin <bar...@genuity.net>
Date: Fri, 27 Dec 2002 20:02:10 GMT
Local: Fri, Dec 27 2002 3:02 pm
Subject: Re: remove the first element from a vector
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In article <aui9kv$kv...@newsreader.mailgate.org>,
Cristina Ghirlanda  <cri...@NOSPAM.interfree-DOT-it> wrote:

>Hi,

>  I wrote a function that removes the first element from a vector, but
>  I think it's not the typical way people write in lisp.

>(defun remove-first-from-vector (vector)
>  (let (new-vector)
>    (do ((index (1- (array-dimension vector 0)) (1- index)))
>        ((= index 0) (concatenate 'vector new-vector))
>      (push (aref vector index) new-vector))))  

>  I would like to hear some advice on how I can write it in a
>  more lispy way. Thanks.

Here are a couple of obvious ways.

(defun remove-first-from-vector (vector)
  (subseq vector 1))

(defun remove-first-from-vector (vector)
  (let ((new-size (1- (array-dimension vector 0)))
        (new-vector (make-array new-size
                                :element-type (array-element-type vector))))
    (dotimes (i new-size)
      (setf (aref new-vector i) (aref vector (1+ i))))
    new-vector))

--
Barry Margolin, bar...@genuity.net
Genuity, Woburn, MA
*** DON'T SEND TECHNICAL QUESTIONS DIRECTLY TO ME, post them to newsgroups.
Please DON'T copy followups to me -- I'll assume it wasn't posted to the group.


 
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Gabe Garza  
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 More options Dec 27 2002, 3:17 pm
Newsgroups: comp.lang.lisp
From: Gabe Garza <g_ga...@ix.netcom.com>
Date: Fri, 27 Dec 2002 20:17:27 GMT
Local: Fri, Dec 27 2002 3:17 pm
Subject: Re: remove the first element from a vector
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Cristina Ghirlanda <cri...@NOSPAM.interfree-DOT-it> writes:
> Hi,

>   I wrote a function that removes the first element from a vector, but
>   I think it's not the typical way people write in lisp.

> (defun remove-first-from-vector (vector)
>   (let (new-vector)
>     (do ((index (1- (array-dimension vector 0)) (1- index)))
>         ((= index 0) (concatenate 'vector new-vector))
>       (push (aref vector index) new-vector))))  

>   I would like to hear some advice on how I can write it in a
>   more lispy way. Thanks.

I'd write it like this:

(defun remove-first-from-vector (vector)
  (subseq vector 1))

And if SUBSEQ didn't exist, I'd write it like this:

(defun remove-first-from-vector (vector)
  (let ((new-vector (make-array
                     (list (1- (length vector)))
                     :element-type (array-element-type vector))))
    (loop for index from 1 below (length vector)
      do (setf (aref new-vector (1- index)) (aref vector index)))
    new-vector))

Gabe Garza      


 
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Pascal Costanza  
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 More options Dec 27 2002, 3:58 pm
Newsgroups: comp.lang.lisp
From: Pascal Costanza <costa...@web.de>
Date: Fri, 27 Dec 2002 21:58:49 +0100
Local: Fri, Dec 27 2002 3:58 pm
Subject: Re: remove the first element from a vector
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Hi Cristina,

Try the function subseq - it can be found in chapter 17 on sequences in
the HyperSpec, or chapter 14 in cltl2.

All the best,
Pascal

Cristina Ghirlanda wrote:
> Hi,

>   I wrote a function that removes the first element from a vector, but
>   I think it's not the typical way people write in lisp.

[...]

--
Given any rule, however ‘fundamental’ or ‘necessary’ for science, there
are always circumstances when it is advisable not only to ignore the
rule, but to adopt its opposite. - Paul Feyerabend


 
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Pascal Bourguignon  
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 More options Dec 27 2002, 10:13 pm
Newsgroups: comp.lang.lisp
From: Pascal Bourguignon <p...@informatimago.com>
Date: 28 Dec 2002 04:13:52 +0100
Local: Fri, Dec 27 2002 10:13 pm
Subject: Re: remove the first element from a vector
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Cristina Ghirlanda <cri...@NOSPAM.interfree-DOT-it> writes:
> Hi,

>   I wrote a function that removes the first element from a vector, but
>   I think it's not the typical way people write in lisp.

> (defun remove-first-from-vector (vector)

And remember that  if you have to remove a lot  of first elements from
vector, it may be more efficient to use a list instead and use CDR.

--
__Pascal_Bourguignon__                   http://www.informatimago.com/
----------------------------------------------------------------------
There is a fault in reality. do not adjust your minds. -- Salman Rushdie


 
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Daniel Barlow  
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 More options Dec 30 2002, 1:34 pm
Newsgroups: comp.lang.lisp
From: Daniel Barlow <d...@telent.net>
Date: Mon, 30 Dec 2002 02:30:14 +0000
Local: Sun, Dec 29 2002 9:30 pm
Subject: Re: remove the first element from a vector
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Gabe Garza <g_ga...@ix.netcom.com> writes:
> Cristina Ghirlanda <cri...@NOSPAM.interfree-DOT-it> writes:
>>   I wrote a function that removes the first element from a vector, but
>>   I think it's not the typical way people write in lisp.
[...]
> I'd write it like this:

> (defun remove-first-from-vector (vector)
>   (subseq vector 1))

> And if SUBSEQ didn't exist, I'd write it like this:

[...]

You don't specify whether a destructive implementation is allowed (or
desired).  If so, you could also use REPLACE

(defun remove-first-from-vector (vector)
  (replace vector vector :start2 1))

-dan

--

   http://www.cliki.net/ - Link farm for free CL-on-Unix resources


 
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