From: Robert Dober <robert.dober@...>
Date: 2006-09-14T05:13:30+09:00
Subject: Re: How to collect over two arrays then look back to one?

------=_Part_52044_16612211.1158178371533
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: quoted-printable
Content-Disposition: inline

On 9/13/06, Jason Nordwick <jason@adapt.com> wrote:
>
> I think...
>
> a.values_at(*(0...a.size).to_a.select {|i| f(a[i]) && g([i-3,0].max..[i+3=
,
> a.size-1].min)})


I am afraid this does not what you want, select returns i's not the value o=
f
the block
you had some great ideas I have stolen below though :)
I'll try to fix your interpretation, ah I see you think he just wants the
indicies, so your solution is (almost) great, you can use [*0..a.size] but
you might have a problem with f(nil) so use
[*0..a.size-1]
OP also stated he wanted g(b[something]) not g(something) it is a riddle
an alternative might be
b.values_at([*0..a.size-1].select{|i|f a[i]}.map{|i|
g(b.values_at(*[*(i-n)..(i+n)].reject
etc. etc.

Ruby seems a little verbose on this one.
>
> -j



I still think OP thaught g to be something abstract so I would write

def ranges a, b, n, &block
### The following is what you were asking for ;)
    b.values_at(
    *(0..a.length-1).select{|i|  block.call(a[i]) }.map{|i| [*(i-n)..(i+n)]
}.
    flatten.uniq.reject{|i|i<0}).compact

end

thanks to your ideas letting me see my stupid mistakes..

Robert

Peter Booth wrote:
> > I am reading Ruby for Rails and Ruby Cookbock and delighted by the
> > Array#find_all and Enumerable#collect methods. I'm wondering what the
> > idiomatic way to do the following is?
> >
> > Two parallel arrays A, B . For each element n of A for which f(An) is
> true,
> > is g(B[n-3:n+3]) true? Where B[n-3:n+3] refers to seven elements of B
> whose
> > position is centered over An' position.
> >
> > Can the block inside Enumerable#collect know it's position inside the
> > Enumerable? Can one collect two parallel arrays?
> >
> > Peter
> >
> -------------------------------------------------------------------------=
---
> > ----------------------------------------
> >
> > The information contained in and accompanying this communication is
> strictly
> > confidential and intended solely for the use of the intended
> recipient(s).
> > If you have received it by mistake please let us know by reply and then
> > delete it from your system; you should not copy the message or disclose
> its
> > content to anyone.
> > MarketAxess reserves the right to monitor the content of emails sent to
> or
> > from its systems.
> > Any comments or statements made are not necessarily those of
> MarketAxess.
> > For more information, please visit www.marketaxess.com. MarketAxess
> Europe
> > Limited is regulated in the UK by the FSA, registered in England no.
> > 4017610, registered office at 71 Fenchurch Street, London, EC3M 4BS.
> > Telephone (020) 7709 3100.
> > MarketAxess Corporation is regulated in the USA by the SEC and the NASD=
,
> > incorporated in Delaware, executive offices at 140 Broadway, New York,
> NY
> > 10005. Telephone (1) 212 813 6000.
> >
> >
>
>
>


--=20
Deux choses sont infinies : l'univers et la b=EAtise humaine ; en ce qui
concerne l'univers, je n'en ai pas acquis la certitude absolue.

- Albert Einstein

------=_Part_52044_16612211.1158178371533--