Ruby even / odd element of an array

[Thong Kuah]

Hi all,

Here's a ruby question. I've tried my google fu but I can't really find the right term for it. Is there an Array or Enumerable method to do this?

I want to get elements 0, 2, 4 first. and then display elements 1,3

a = [a, b, c, d]  #some array
a.each_with_index do |item, index|
  next if index.odd?
  p item
end

a.each_with_index do |item, index|
  next if index.even?
  p item
end


--
Best regards,
Y. Thong Kuah

[Henry Maddocks]

On 29/08/2008, at 1:38 PM, Thong Kuah wrote:

> Hi all,
>
> Here's a ruby question. I've tried my google fu but I can't really
> find the right term for it. Is there an Array or Enumerable method
> to do this?
>
> I want to get elements 0, 2, 4 first. and then display elements 1,3

a.partition {|obj| a.index(obj) % 2 == 0}
=> [["a", "c"], ["b", "d"]]

might not work if obj repeats

[Henry Maddocks]

On 29/08/2008, at 1:38 PM, Thong Kuah wrote:

> Hi all,
>
> Here's a ruby question. I've tried my google fu but I can't really
> find the right term for it. Is there an Array or Enumerable method
> to do this?
>
> I want to get elements 0, 2, 4 first. and then display elements 1,3

Righteous hack alert!

a = %w( a b c d)
=> ["a", "b", "c", "d"]
h = Hash[*a]
=> {"a"=>"b", "c"=>"d"}
irb(main):012:0> h.keys
=> ["a", "c"]
irb(main):013:0> h.values
=> ["b", "d"]

[Tim Haines]

That's sexy.

[Philip Murray]

On 29/08/2008, at 1:38 PM, Thong Kuah wrote:

101 Ways to skin a cat

arr = [ :a, :x, :b, :y, :c, :z ]
odds = []
evens = []

arr.each_with_index { |v,i| (i.odd? ? odds : evens) << v }

Cheers

Phil

[Tim Haines]

Only problem is that a hash's keys and values aren't guaranteed to retain their order..

Tim.

On Fri, Aug 29, 2008 at 1:51 PM, Henry Maddocks <henry.m...@gmail.com> wrote:

[Philip Murray]

On 29/08/2008, at 1:54 PM, Tim Haines wrote:

Only problem is that a hash's keys and values aren't guaranteed to retain their order..

Tim.

They are in Ruby 1.9! :P

[Henry Maddocks]

On 29/08/2008, at 1:54 PM, Tim Haines wrote:

> Only problem is that a hash's keys and values aren't guaranteed to
> retain their order..

Good point. It might until you add something to the hash which you
wouldn't in this case. It's still a hack though. I think Phil's
solution is the best.

[Tim Uckun]

On Fri, Aug 29, 2008 at 1:51 PM, Henry Maddocks
<henry.m...@gmail.com> wrote:
>
>

Won't work if there are an odd number of elements in the array.

[Thong Kuah]

101 Ways to skin a cat

arr = [ :a, :x, :b, :y, :c, :z ]
odds = []
evens = []

arr.each_with_index { |v,i| (i.odd? ? odds : evens) << v }

Cheers

Phil

That seems to be the best way so far. Monkeypatching array, we'll get

class Array
 def odd_elements
    arr=[]
    self.each_with_index {|v,i| arr << v if i % 2 !=0 }
    arr
 end
end

irb(main):016:0> arr = [ :a, :x, :b, :y, :c, :z ]

=> [:a, :x, :b, :y, :c, :z]

irb(main):017:0> arr.odd_elements
=> [:x, :y, :z]

[mic...@diaspora.gen.nz]

>That seems to be the best way so far. Monkeypatching array, we'll get
>
>class Array
> def odd_elements
> arr=[]
> self.each_with_index {|v,i| arr << v if i % 2 !=0 }
> arr
> end
>end

Why bother with the arr variable?

self.zip((1..self.length).to_a).
select {|v,i| i % 2 == 1}.
collect {|v,i| v}

(I think I've been polluted with programming in Haskell recently; I
keep trying to be point-free.)

-- michael

[Henry Maddocks]

See now your changing the requirements. The problem used to be odd AND
even. Even only is much simpler. It's lucky we're all so damn agile.

Henry

PS Haskell, pfffffftttttttt