Velocity Reviews > Ruby > find previous & next in array

# find previous & next in array

John Griffiths
Guest
Posts: n/a

 05-14-2009
hi, anyone know how to do this?

basically i've got an array of items

a = ['a','b','c','d']

now given i can find the position of say 'c' using .index('c'), how do i
get the positions of the ones previous & next to it.

a recursive routine would probably do it, but looking for something more
flash

any ideas?
--
Posted via http://www.ruby-forum.com/.

Boby Selamet Hartono
Guest
Posts: n/a

 05-14-2009
[Note: parts of this message were removed to make it a legal post.]

2009/5/14 John Griffiths <(E-Mail Removed)>

> hi, anyone know how to do this?
>
> basically i've got an array of items
>
> a = ['a','b','c','d']
>
> now given i can find the position of say 'c' using .index('c'), how do i
> get the positions of the ones previous & next to it.
>
> a recursive routine would probably do it, but looking for something more
> flash
>
> any ideas?
> --
> Posted via http://www.ruby-forum.com/.
>
>

a[a.index(:c)-1] or a[a.index(:c)+1]?

--
Tidak ada yang lebih baik dari kembali ke asal
Nothing can be better than back to the roots

Joshua Collins
Guest
Posts: n/a

 05-14-2009
[Note: parts of this message were removed to make it a legal post.]

a[a.index(:c)+1]

it is:

a[a.index('c')+1]

On Wed, May 13, 2009 at 11:48 PM, Boby Selamet Hartono
<(E-Mail Removed)>wrote:

> 2009/5/14 John Griffiths <(E-Mail Removed)>
>
> > hi, anyone know how to do this?
> >
> > basically i've got an array of items
> >
> > a = ['a','b','c','d']
> >
> > now given i can find the position of say 'c' using .index('c'), how do i
> > get the positions of the ones previous & next to it.
> >
> > a recursive routine would probably do it, but looking for something more
> > flash
> >
> > any ideas?
> > --
> > Posted via http://www.ruby-forum.com/.
> >
> >

> a[a.index(:c)-1] or a[a.index(:c)+1]?
>
> --
> Tidak ada yang lebih baik dari kembali ke asal
> Nothing can be better than back to the roots
>

Boby Selamet Hartono
Guest
Posts: n/a

 05-14-2009
[Note: parts of this message were removed to make it a legal post.]

2009/5/14 Joshua Collins <(E-Mail Removed)>

> Boby had it almost right!
>
>
> a[a.index(:c)+1]
>
> it is:
>
> a[a.index('c')+1]
>
>
>
> On Wed, May 13, 2009 at 11:48 PM, Boby Selamet Hartono
> <(E-Mail Removed)>wrote:
>
> > 2009/5/14 John Griffiths <(E-Mail Removed)>
> >
> > > hi, anyone know how to do this?
> > >
> > > basically i've got an array of items
> > >
> > > a = ['a','b','c','d']
> > >
> > > now given i can find the position of say 'c' using .index('c'), how do

> i
> > > get the positions of the ones previous & next to it.
> > >
> > > a recursive routine would probably do it, but looking for something

> more
> > > flash
> > >
> > > any ideas?
> > > --
> > > Posted via http://www.ruby-forum.com/.
> > >
> > >

> > a[a.index(:c)-1] or a[a.index(:c)+1]?
> >
> > --
> > Tidak ada yang lebih baik dari kembali ke asal
> > Nothing can be better than back to the roots
> >

>

It was a copy from my irb. I'm use symbols as objects in my array. I've
never use index method but since I figure out that method returns an Integer
I think it would be something like that (thanks to irb). I'm a newbie and
just joining this ML yesterday .

--
Tidak ada yang lebih baik dari kembali ke asal
Nothing can be better than back to the roots

Robert Klemme
Guest
Posts: n/a

 05-14-2009
2009/5/14 John Griffiths <(E-Mail Removed)>:
> hi, anyone know how to do this?
>
> basically i've got an array of items
>
> a = ['a','b','c','d']
>
> now given i can find the position of say 'c' using .index('c'), how do i
> get the positions of the ones previous & next to it.
>
> a recursive routine would probably do it, but looking for something more
> flash
>
> any ideas?

Depends on what you need to do. Do you need those indexes or do you

There are a few variants, but the nice ones aren't really safe against
edge cases (first and last element):

irb(main):004:0> a = ['a','b','c','d']
=> ["a", "b", "c", "d"]
irb(main):005:0> i = a.index('c') and a[i-1 .. i+1]
=> ["b", "c", "d"]
irb(main):006:0> a[a.index('c') - 1, 3] rescue nil
=> ["b", "c", "d"]
irb(main):007:0> i = a.index('a') and a[i-1 .. i+1]
=> []
irb(main):008:0> a[a.index('a') - 1, 3] rescue nil
=> ["d"]

The safest is probably

i = a.index('c')

if i
predecessor = i > 0 ? a[i -1] : nil
successor = a[i + 1] # safe!
end

Or as a variant

i = a.index('c') and begin
predecessor = i > 0 ? a[i -1] : nil
successor = a[i + 1] # safe!
end

Kind regards

robert

--
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/

John Griffiths
Guest
Posts: n/a

 05-14-2009
> The safest is probably
>
> i = a.index('c')
>
> if i
> predecessor = i > 0 ? a[i -1] : nil
> successor = a[i + 1] # safe!
> end
>
> Or as a variant
>
> i = a.index('c') and begin
> predecessor = i > 0 ? a[i -1] : nil
> successor = a[i + 1] # safe!
> end
>
> Kind regards
>
> robert

thanks Robert, i was trying to build up a little function to find the
prev/next elements in an array, thanks to your help it's sorted;
couldn't find a solution online. appreciate it all.

John.
--
Posted via http://www.ruby-forum.com/.

Joshua Collins
Guest
Posts: n/a

 05-14-2009
[Note: parts of this message were removed to make it a legal post.]

Bobby, I am new too, so I might be missing something as well.

I tried your method first, and when I tried to do the symbol in irb it gave
an error. Maybe you have settings I do not?

On Thu, May 14, 2009 at 11:38 AM, John Griffiths <(E-Mail Removed)>wrote:

> > The safest is probably
> >
> > i = a.index('c')
> >
> > if i
> > predecessor = i > 0 ? a[i -1] : nil
> > successor = a[i + 1] # safe!
> > end
> >
> > Or as a variant
> >
> > i = a.index('c') and begin
> > predecessor = i > 0 ? a[i -1] : nil
> > successor = a[i + 1] # safe!
> > end
> >
> > Kind regards
> >
> > robert

>
> thanks Robert, i was trying to build up a little function to find the
> prev/next elements in an array, thanks to your help it's sorted;
> couldn't find a solution online. appreciate it all.
>
>
> John.
> --
> Posted via http://www.ruby-forum.com/.
>
>