Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!crdgw1!altair!halvers
From: halvers@altair.crd.ge.com (Pete Halverson)
Newsgroups: comp.lang.lisp
Subject: Re: another question, arrays
Message-ID: <20101@crdgw1.crd.ge.com>
Date: 31 May 91 13:56:45 GMT
References: <43929@netnews.upenn.edu> <13228@ptolemy-ri.arc.nasa.gov>
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Reply-To: halverson@crd.ge.com (Pete Halverson)
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In article <13228@ptolemy-ri.arc.nasa.gov> chucko@ptolemy.arc.nasa.gov (Chuck Fry) writes:
>In article <43929@netnews.upenn.edu> vinson@linc.cis.upenn.edu (Jack Vinson) writes:

>>Me again,  I am also playing with arrays for the first time in lisp and am
>>wondering what kind of interesting functions there are for messing with them.
>>In particular I will be frequently updating one array by moving elements down
>>into the array.  ie if the array is (1.2 1.1 1.2 1.3 1.1 1.0) and new data is
>>1.2 I want to put the new info at the 'beginning' of the array and shift
>>everything down, so I would get (1.2 1.2 1.1 1.2 1.3 1.1) with the last
>>element knocked off.  The way I know how to do this is with a do-loop
>>that copies element i into i+1, starting from the highest element.
>
>CLtL provides a facility for dealing with vectors (simple arrays) as
>stacks [using VECTOR-PUSH and VECTOR-POP].

>If the most recent must be the 0th element, you're pretty much stuck
>with the DO-loop approach.

You can also use the REPLACE function to shift stuff around, e.g.
  
    (replace my-array my-array :start1 1)

should behave the same as

  (loop for i from (1- (length my-array)) downto 1
        do (setf (aref my-array i) (aref my-array (1- i))))

and is hopefully (?) better optimized.

Pete
      
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Pete Halverson                                      INET: halverson@crd.ge.com 
GE Corporate R&D Center                       UUCP: uunet!crd.ge.com!halverson
Schenectady, NY