[prev in list] [next in list] [prev in thread] [next in thread] 

List:       racket-users
Subject:    [plt-scheme] Newbie map question
From:       robby () cs ! uchicago ! edu (Robby Findler)
Date:       2004-12-30 13:33:29
Message-ID: 20041230133330.58A8F6C8FE () laime ! cs ! uchicago ! edu
[Download RAW message or body]

I think you're looking for the function apply.

Robby

At Thu, 30 Dec 2004 13:22:41 +0100, Francisco Jes?s Mart?nez Serrano wrote:
>   For list-related administrative tasks:
>   http://list.cs.brown.edu/mailman/listinfo/plt-scheme
> 
> Hi, i'm learning scheme "the hard way", making a school project.
> 
> I need to manipulate vectors and do some basic vector algebra.
> 
> When faced with something as 'trivial' as the sum, I know I can sum
> vectors (lists) just as this:
> 
> (map + '(1 2 3) '(4 5 6) '(4 5 6))
> 
> The problem of this approach is that map + is not a procedure I can
> pass as an argument to a function (inner or outer product, for
> example), i need a self-contained map+. I can do this just by
> defining:
> 
> (define map+
>   (lambda (v1 v2)
>     (map + v1 v2)))
> 
> The problem of this approach is that it only works with 2 arguments. I
> know I can iterate through the list of vectors and accomplish it, but
> that seems too inefficient when a simple map + will do. Something like
> this:
> 
> (define map+
>   (lambda vecs
>     (map + vecs)))
> 
> or better:
> 
> (define elementwise
>   (lambda (f)
>     (lambda vecs
>       (map f vecs))))
> 
> (define map+ (elementwise +))
> 
> Which doesn't work because vecs is a list of vectors, and map expects
> each vector as an argument
> 
> I know it's very simple, but can somebody give me a clue?
> 
> Thanks.



[prev in list] [next in list] [prev in thread] [next in thread]