Cyclic array

Ruby
1

I would like to print n elements from an Array in a cyclic way.

I mean :

using anArray = [ “a”, “b”, “c”, “d”, “e”, “f”, “g”], I should do :

anArray.print_cyclic(4, 0) => “a”, “b”, “c”, “d” (first print 4
elements starting with the first one)

anArray.print_cyclic_next => “b”, “c”, “d”, “e”
anArray.print_cyclic_next => “c”, “d”, “e”, “f”
anArray.print_cyclic_next => “d”, “e”, “f”, “g”
anArray.print_cyclic_next => “e”, “f”, “g”, “a”
anArray.print_cyclic_next => “f”, “g”, “a”, “b”
anArray.print_cyclic_next => “g”, “a”, “b”, “c”
…
also in reverse cycle
anArray.print_cyclic(4, 0) => “a”, “b”, “c”, “d”
anArray.print_cyclic_previous => “g”, “a”, “b”, “c”
anArray.print_cyclic_previous => “f”, “g”, “a”, “b”,

what could be the simplest way to do it ? no simple way using Array
class methods only ,
should I define a class and methods to loop into the array ? any
existing lib ? if it has been already done why should I rewrite it …

tfyh

joss

2

On Apr 28, 2007, at 10:10 PM, Josselin wrote:

anArray.print_cyclic_next => “c”, “d”, “e”, “f”
what could be the simplest way to do it ? no simple way using
Array class methods only ,
should I define a class and methods to loop into the array ? any
existing lib ? if it has been already done why should I rewrite
it …

tfyh

joss

sounds like classic (?) Ruby. you just need a block. in the block,
get the array size, move element 0 to end. do block until satisfied.

3

On 4/28/07, Josselin [email protected] wrote:

anArray.print_cyclic_next => “b”, “c”, “d”, “e”

This will do the shifting but I’m not sure about wrapping around.

require ‘enumerator’
(1…25).each_cons(5) do |x|
p x
end

Harry

4

On Apr 28, 7:05 am, Josselin [email protected] wrote:

I would like to print n elements from an Array in a cyclic way.

Not a direct answer to your question, but regarding circular lists
(which can be created from an array):
http://phrogz.net/RubyLibs/rdoc/files/Ouroboros_rb.html

5

On 2007-04-28 15:05:48 +0200, Josselin [email protected] said:

anArray.print_cyclic_next => “c”, “d”, “e”, “f”
what could be the simplest way to do it ? no simple way using Array
class methods only ,
should I define a class and methods to loop into the array ? any
existing lib ? if it has been already done why should I rewrite it …

tfyh

joss

Thanks to all of u . As always different ways … the most difficult
step for a newbie is : where should I start ?

joss

6

On Apr 28, 2007, at 3:10 PM, Josselin wrote:

anArray.print_cyclic_next => “c”, “d”, “e”, “f”
what could be the simplest way to do it ? no simple way using
Array class methods only ,
should I define a class and methods to loop into the array ? any
existing lib ? if it has been already done why should I rewrite
it …

This is a possible approach:

module Enumerable
def each_cycle(window, start=0)
(start…length+start).each do |i|
yield((i…i+window).map {|n| self[n % length]})
end
end
end

Usage is:

a = [ “a”, “b”, “c”, “d”, “e”, “f”, “g”]
a.each_cycle(4) do |cycle|
puts “#{cycle}”
end

You can delegate reverse cycle to each_cycle on the reverse (and
perhaps taking the opposite of start mod length, depending on the
meaning of start).

– fxn

7

On Apr 29, 2007, at 12:10 AM, Josselin wrote:

anArray.print_cyclic_next => “e”, “f”, “g”, “a”
existing lib ? if it has been already done why should I rewrite
it …
tfyh
joss

Thanks to all of u . As always different ways … the most difficult
step for a newbie is : where should I start ?

joss
Indeed, as a newbie myself, (forever I think) it is often a bit
overwhelming where to start.
A common method is to sit down with pen and paper and write out the
ideas, brainstorming. Figure out what you want to do. then break each
part down into it’s components. it doesn’t have to be in code yet.
That’s almost the easy fun part, translating your ideas into code.
It really is a design process. Some snippets that you create or do
often enough will stick in your mind and you’ll be able to apply them
quicker with practice. But pseudo code is always a good thing, if you
comment it out, it is instant documentation! (if necessary.

8

On 4/28/07, Josselin [email protected] wrote:

what could be the simplest way to do it ? no simple way using Array
class methods only ,

Try something like this.

arr = (“a”…“g”).to_a
(1…25).each do |d|
arr.push << arr.shift
p arr.slice(0…5)
end

Harry

9

what could be the simplest way to do it ? no simple way using Array
class methods only ,

Sorry for the double post.
In my mail the code got chopped off at the bottom.

Try this.

arr = (“a”…“g”).to_a
(1…25).each do |d|
arr.push << arr.shift
p arr.slice(0…5)
end

Harry

10

what could be the simplest way to do it ? no simple way using Array
class methods only ,

I did a poor job of cleaning that code.
It had unnecessary stuff in it.
Sorry, my brain is not working today.

arr = (“a”…“g”).to_a
(1…25).each do
arr << arr.shift
p arr.slice(0…5)
end

Harry

11

Xavier N. wrote:
…

module Enumerable
def each_cycle(window, start=0)
(start…length+start).each do |i|
yield((i…i+window).map {|n| self[n % length]})
end
end
end

Here is a slight variation, for amusement, but it doesn’t work for
window > length:

module Enumerable
def each_cycle(window, start = 0)
(-length+start…start).each do |i|
yield values_at(*(i…i+window))
end
end
end

a = [ “a”, “b”, “c”, “d”, “e”, “f”, “g”]
a.each_cycle(4) do |cycle|
puts “#{cycle}”
end

a.each_cycle(14) do |cycle|
puts “#{cycle}”
end

END

abcde
bcdef
cdefg
defga
efgab
fgabc
gabcd

abcdefgabcdefg
bcdefgabcdefg
cdefgabcdefg
defgabcdefg
efgabcdefg
fgabcdefg
gabcdefg

12

On Apr 28, 7:58 am, Phrogz [email protected] wrote:

On Apr 28, 7:05 am, Josselin [email protected] wrote:

I would like to print n elements from an Array in a cyclic way.

Not a direct answer to your question, but regarding circular lists
(which can be created from an array):
File: Ouroboros.rb

Expanding on its usage for the stated problem:

irb(main):001:0> require ‘Ouroboros.rb’
=> true
irb(main):002:0> anArray = [ “a”, “b”, “c”, “d”, “e”, “f”, “g”]
=> [“a”, “b”, “c”, “d”, “e”, “f”, “g”]
irb(main):003:0> aSnake = Ouroboros.from_a anArray
=> #<Ouroboros:0x367810 @current_index=0, @current=“a”, @all=[“a”,
“b”, “c”, “d”, “e”, “f”, “g”], @size=7>
irb(main):004:0> aSnake.to_a[ 0…4 ]
=> [“a”, “b”, “c”, “d”]
irb(main):005:0> aSnake.increment
=> [“b”]
irb(main):006:0> aSnake.to_a[ 0…4 ]
=> [“b”, “c”, “d”, “e”]
irb(main):008:0> aSnake.increment
=> “c”
irb(main):009:0> aSnake.to_a[ 0…4 ]
=> [“c”, “d”, “e”, “f”]

…and so on.

13

On Apr 30, 2007, at 3:43 AM, Rick DeNatale wrote:

 end

end

This method won’t work for Enumerables in general, although I guess it
does work for Arrays.

Not all enumerables have one or both length or [] methods.

Oh right, thank you. I don’t know why ri Enumerable lists length
here, looks like it is getting non-core methods from somewhere else.
I overlooked [] though. The OP wanted this for an Array, it would
certainly work there.

– fxn

14

On 4/28/07, Xavier N. [email protected] wrote:

This is a possible approach:

module Enumerable
def each_cycle(window, start=0)
(start…length+start).each do |i|
yield((i…i+window).map {|n| self[n % length]})
end
end
end

This method won’t work for Enumerables in general, although I guess it
does work for Arrays.

Not all enumerables have one or both length or [] methods.

–
Rick DeNatale

My blog on Ruby
http://talklikeaduck.denhaven2.com/

15

On Apr 30, 2007, at 11:13 AM, Xavier N. wrote:

This method won’t work for Enumerables in general, although I
guess it
does work for Arrays.

Not all enumerables have one or both length or [] methods.

Oh right, thank you. I don’t know why ri Enumerable lists length
here, looks like it is getting non-core methods from somewhere
else. I overlooked [] though. The OP wanted this for an Array, it
would certainly work there.

By “there” I mean defining that method in Array, leaving the
definition in Enumerable is broken.

– fxn

16

On 4/30/07, Xavier N. [email protected] wrote:

     yield((i..i+window).map {|n| self[n % length]})

here, looks like it is getting non-core methods from somewhere else.
I overlooked [] though. The OP wanted this for an Array, it would
certainly work there.

By the way I think that there’s a typo that should be an open range in
the yield expression, otherwise you get

 yield((i...i+window).map {|n| self[n % length]})

Thinking about the Enumerable vs. Array aspect of this got me thinking
abou the subtleties of duck typing leading to another blog entry:

http://talklikeaduck.denhaven2.com/articles/2007/04/30/our-kind-of-ducks-odd-ducks-and-trained-ducks

–
Rick DeNatale

My blog on Ruby
http://talklikeaduck.denhaven2.com/

17

On Apr 30, 2007, at 11:13 AM, Xavier N. wrote:

     yield((i..i+window).map {|n| self[n % length]})

Oh right, thank you. I don’t know why ri Enumerable lists length here
It took me a while to discover where that non-core Enumerable#length
reported by ri/fri comes from, it is defined by RGL in the file

rgl-0.2.3/lib/rgl/base.rb

I’ve learned that ri offers --system the hard way :-).

– fxn

18

On May 1, 2007, at 9:05 AM, Xavier N. wrote:

 end

It took me a while to discover where that non-core
Enumerable#length reported by ri/fri comes from, it is defined by
RGL in the file

rgl-0.2.3/lib/rgl/base.rb

I’ve learned that ri offers --system the hard way :-).

– fxn

For those who aren’t reading Rick’s blog (where this is now in a
comment):

module Enumerable
def each_cycle(window, start=0)
wrap_start = []
cache = []
each_with_index do |e,i|
cache << e
if i >= start + (window - 1)
yield cache[start, window]
cache.shift
else
wrap_start << e
end
end
wrap_start.each do |e|
cache << e
yield cache[start, window]
cache.shift
end
self
end
end

Then you can each_cycle anything that is Enumerable, like a Range:

(1…5).each_cycle(3) {|x| p x}
[1, 2, 3]
[2, 3, 4]
[3, 4, 5]
[4, 5, 1]
[5, 1, 2]
=> 1…5
{ ‘dog’ => ‘Rover’, ‘cat’ => ‘Mittens’, ‘fish’ =>
‘Goldie’ }.each_cycle(2) {|x| p x}
[[“cat”, “Mittens”], [“fish”, “Goldie”]]
[[“fish”, “Goldie”], [“dog”, “Rover”]]
[[“dog”, “Rover”], [“cat”, “Mittens”]]
=> {“cat”=>“Mittens”, “fish”=>“Goldie”, “dog”=>“Rover”}

-Rob

Rob B. http://agileconsultingllc.com
[email protected]