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.
One solution is to just use a gigantic array which I just add new data to the
end of, but this seems like it might waste space ~time~. Which is more
expensive, keeping track of five 20x2 arrays the above way or creating five
5000x2 arrays and adding data from the beginning?
Jack
Jack Vinson ······@linc.cis.upenn.edu
In article <·····@netnews.upenn.edu> ······@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. If you don't mind the nth element of the array being most
recent instead of the 0th, you can use VECTOR-PUSH or
VECTOR-PUSH-EXTEND on an array with a fill-pointer.
VECTOR-PUSH-EXTEND adjusts the array if the initial array size is
exceeded, providing you created the array with :ADJUSTABLE T to begin
with.
Then VECTOR-POP can destructively access the most recent element, or
(AREF stack (1- (FILL-POINTER stack)))
will do the same thing non-destructively.
If the most recent must be the 0th element, you're pretty much stuck
with the DO-loop approach.
Chuck Fry ······@Charon.ARC.NASA.GOV ...ames!ptolemy!chucko
Disclaimer: No one but me is responsible for this misinformation.
"Sun is in an ideal situation. It has convinced the market that open
technology is the best. Yet, the company narrows its own interpretation
of 'open' as its market share and technology advantages expands."
-- "The Fifth Architecture", Mark Hall, in SunWorld, April 1991
From: Pete Halverson
Subject: Re: another question, arrays
Date:
Message-ID: <20101@crdgw1.crd.ge.com>
In article <·····@ptolemy-ri.arc.nasa.gov> ······@ptolemy.arc.nasa.gov (Chuck Fry) writes:
>In article <·····@netnews.upenn.edu> ······@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
--
===============================================================================
Pete Halverson INET: ·········@crd.ge.com
GE Corporate R&D Center UUCP: uunet!crd.ge.com!halverson
Schenectady, NY