From: ao tianlong <aotianlong@...>
Date: 2006-11-29T14:31:22+09:00
Subject: Re: array question

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2006/11/23, William James <w_a_x_man@yahoo.com>:
>
> Robert Klemme wrote:
> > On 21.11.2006 10:16, William James wrote:
> > > Robert Klemme wrote:
> > >> On 21.11.2006 08:18, William James wrote:
> > >>> Li Chen wrote:
> > >>>> Hi all,
> > >>>>
> > >>>> I want to build a new array from an old one with every element
> being
> > >>>> duplicated except the first and last element. And here are my
> codes. I
> > >>>> wonder if this is a real Ruby way to do it.
> > >>>>> array=[1,2,3,4,5,6,7,8,9,10]
> > >>> => [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
> > >>>>> array.zip(array).flatten[1..-2]
> > >>> => [1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8, 8, 9, 9, 10]
> > >> That's cute!  I have another one with #inject (of course):
> > >>
> > >> irb(main):007:0> arr=(1..10).to_a
> > >> => [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
> > >> irb(main):008:0> copy=[]
> > >> => []
> > >> irb(main):009:0> arr.inject{|a,b| copy << a << b; b}
> > >> => 10
> > >> irb(main):010:0> copy
> > >> => [1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8, 8, 9, 9, 10]
> > >
> > > This demonstrates an excellent understanding of inject and
> >
> > Thank you!
> >
> > > is a good way to eliminate the somewhat ugly [1..-2].
> >
> > Well, you can use [1...-1] instead. :-)
>
> Ha, ha.  Also ugly.
>
> >
> > > Here's a prolix way of avoiding array indexing while using zip:
> > >
> > > copy=arr.dup; copy.shift; copy.pop
> > > arr.zip(copy).flatten.compact
> >
> > You can copy and reduce in one step:
> >
> >  >> arr=(1..10).to_a
> > => [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
> >  >> arr.zip(arr[1...-1]).flatten.compact
> > => [1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8, 8, 9, 9, 10]
> >
> > Or, more efficient
> >
> >  >> arr.zip(arr[1...-1]).flatten!.compact!
> > => [1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8, 8, 9, 9, 10]
>
> But it has "[1...-1]"!  Indexing with literal numbers is so horrid.
>
> >
> > Cheers
> >
> >       robert





your name looks like a chinese , and i'm too.
>
> what about this code ?
>
> irb(main):008:0> %w{a b c d e f g h i j k l m n o p q r s t u v w x y
> z}.map{|i| i = [i,i]}.flatten[1..-2]
> => ["a", "b", "b", "c", "c", "d", "d", "e", "e", "f", "f", "g", "g",
> "h", "h", "i", "i", "j", "j", "k", "k", "l", "l", "m", "m", "n", "n",
> "o", "o", "p", "p", "q", "q", "r", "r", "s", "s", "t", "t", "u", "u",
> "v", "v", "w", "w", "x", "x", "y", "y", "z"]
>

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