From: Farrel Lifson <farrel.lifson@...>
Date: 2006-08-02T16:59:42+09:00
Subject: Re: golfing Eratosthenes

On 02/08/06, Farrel Lifson <farrel.lifson@gmail.com> wrote:
> On 02/08/06, Daniel Baird <danielbaird@gmail.com> wrote:
> > Hi all,
> >
> > I've been golfing around with the sieve of Eratosthenes.  Here's what
> > I've got so far:
> >
> > a=(2..100).to_a;p a.each{|c|a.map!{|d|c&&d&&c<d&&d%c==0?nil:d}}.compact
> >
> > It's already under 80 chars, but I'd still love to remove the
> > definition of the array a, and do the whole thing with no semicolons.
> > Any suggestions?
> >
> > If you're interested, here's an indented/commented copy that might
> > save a few minutes..
> >
> > # create an array of integers, 2 to 100
> > a=(2..100).to_a;
> > p a.each{ |c|
> >   # for each element c in that array, if c isn't nil, it's prime. so
> > set multiples of c to nil
> >   a.map!{ |d|
> >     c && d && c<d && d%c == 0 ? nil : d
> >   }
> > }.compact  # finally, print the array minus the nils
> >
> >
> > I'd appreciate any comments.
> >
> > Cheers
> >
> > ;Daniel
> >
> >
> > --
> > Daniel Baird
> > http://tiddlyspot.com (free, effortless TiddlyWiki hosting)
> > http://danielbaird.com (TiddlyW;nks! :: Whiteboard Koala :: Blog ::
> > Things That Suck)
>
> Here's my attempt. Note that I have made it a bit more general by
> assigning s = 100 beforehand.
>
> (2..(s**0.5)).inject((2..s).to_a){|a,c|a.map!{|d|c&&d&&c<d&&d%c==0?nil:d}}.compact
>
> I got rid of the semi-colons and assigning the arrays (although
> technically it's still 'assigned' in the inject) although it might has
> made it a bit loner.
>
> Farrel
>

Gah! Excuse my atrocious spelling and grammar. "...although it has
made it a bit longer".