Forum: Ruby What about a 'series' type?

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F62d0be4e8209c45a02d4f595014845a?d=identicon&s=25 Peter Marsh (killswitch)
on 2007-06-07 13:00
I'm sure everyone is fimilar with ranges:

(1..10).to_a = [1,2,3,4,5,6,7,8,9,10] (from manual)

But this isn't any good if you want a arithmetic [3,5,7,9] or geometric
[2,6,18,54] series. So I suggest this:


arithmetic_series = Arith.new(First_Term,Common_Difference)

aritmetic_series[9] will then generate the 10th term of the sequence (0
being the first to be consistent) and arithmetic_series[0..9] will
return an array with the first to tenth terms. The same goes for a
geometric series.

gemometric_series = Geometric.new(First_Term,Common_Ratio)


Now, there may be other ways to achieve this, but I think this way is
nicer.
703fbc991fd63e0e1db54dca9ea31b53?d=identicon&s=25 Robert Dober (Guest)
on 2007-06-07 13:30
(Received via mailing list)
On 6/7/07, Peter Marsh <evil_grunger@hotmail.com> wrote:

Honestly I do not believe that the core is the place to put such
things, furthermore I believe it is too specific a feature, a more
general approach might have better chances to be fit for the core; Yet
I do not think what follows is fit for the core either, but maybe you
find it interesting or helpful:

class Lazy
  def initialize init, op, *args
    @init = init
    @op   = op
    @args = args.dup
  end

  def upto value
    return [] if value < 1
    (2..value).inject([@init]){ |acc,| acc << acc.last.send( @op, *@args
) }
  end
end # class Lazy

505/6 > irb -r lazy.rb
irb(main):001:0> l = Lazy.new 1, :+, 2
=> #<Lazy:0xb7ddfa60 @args=[2], @init=1, @op=:+>
irb(main):002:0> l.upto 5
=> [1, 3, 5, 7, 9]
irb(main):003:0> m = Lazy.new 2, :*, 3
=> #<Lazy:0xb7dd4908 @args=[3], @init=2, @op=:*>
irb(main):004:0> m.upto 4
=> [2, 6, 18, 54]
irb(main):005:0>

Cheers
Robert

P.S. Implementations without #inject are theoretically possible ;)
R.
B8cfd5ec0f88bf5b5f2eedda7d1a0746?d=identicon&s=25 unknown (Guest)
on 2007-06-07 14:58
(Received via mailing list)
In message <cd08f63ca2ad51e567d4288410f593da@ruby-forum.com>, Peter
Marsh writes:
>gemometric_series = Geometric.new(First_Term,Common_Ratio)
>
>Now, there may be other ways to achieve this, but I think this way is
>nicer.

These seem like special cases of Series.new([Start Terms], Proc).

(Consider Fibbonacci sequences, for instance, or Pascal's Triangle.)

-s
7b4707f974af261f71943e1f2046c9ee?d=identicon&s=25 SonOfLilit (Guest)
on 2007-06-07 15:18
(Received via mailing list)
Actually, the syntax:

a = Series.new(8) {|i| 5*i**3}

a.collect{|i| i + 1}.select{|i| i % 2 == 0} # i.e. a is an enumerable
object

is quite cool and might be useful in some cases. The only problem I'm
trying to solve is that of providing syntax for persistence (e.g. try
to implement a series of Fibonacci numbers with the iterative
algorithm using this Series syntax). Perhaps an optional hash argument
that is used to give initial values to instance variables?

With persistence, this could be a very useful idiom in many cases, and
maybe even deserves to be stdlib.

Aur
1bac2e65d64faf472cf2ebc94f0f5ee0?d=identicon&s=25 ara.t.howard (Guest)
on 2007-06-07 15:43
(Received via mailing list)
On Jun 7, 2007, at 5:00 AM, Peter Marsh wrote:

>
> nicer.
>
> --
> Posted via http://www.ruby-forum.com/.
>

it can be done with lambdas in ruby on a case by case basis:

cfp:~ > cat a.rb
arithmetic = lambda do |i|
   if i.respond_to? :map
     i.map{|j| arithmetic[j]}
   else
     i >= 1 ? (2 + arithmetic[i-1]) : 1
   end
end

p arithmetic[0]
p arithmetic[1]
p arithmetic[4]

p arithmetic[0..9]


cfp:~ > ruby a.rb
1
3
9
[1, 3, 5, 7, 9, 11, 13, 15, 17, 19]

kind regards.

-a
F62d0be4e8209c45a02d4f595014845a?d=identicon&s=25 Peter Marsh (killswitch)
on 2007-06-07 16:47
SonOfLilit wrote:
> Actually, the syntax:
>
> a = Series.new(8) {|i| 5*i**3}
>
> a.collect{|i| i + 1}.select{|i| i % 2 == 0} # i.e. a is an enumerable
> object
>
> is quite cool and might be useful in some cases. The only problem I'm
> trying to solve is that of providing syntax for persistence (e.g. try
> to implement a series of Fibonacci numbers with the iterative
> algorithm using this Series syntax). Perhaps an optional hash argument
> that is used to give initial values to instance variables?
>
> With persistence, this could be a very useful idiom in many cases, and
> maybe even deserves to be stdlib.
>
> Aur

The two examples I gave are fairly specific, I didn't really think about
that. However, I still think a 'series' type would be useful, even if
the implimentation is different to my example.

Taking prime numbers as an example using the current 'prime' class you
have to use:

require 'mathn'

primes = Prime.new

etc

With a seires type you could do something like this:

primes = Series.new(Starting_value,Some_block_to_define_serires)

primes[0] = 2
primes[0..2]
>> [2,3,5]

Giving definate advantages, I feel.
F62d0be4e8209c45a02d4f595014845a?d=identicon&s=25 Peter Marsh (killswitch)
on 2007-06-07 16:52
> primes = Series.new(Starting_value,Some_block_to_define_serires)

Just wanted to be a bit clearer about this, the second argument is a
block which can generate nth term in a series. This would probally take
a while for primes, but if it were recursive then it would be easier...
E0d864d9677f3c1482a20152b7cac0e2?d=identicon&s=25 Robert Klemme (Guest)
on 2007-06-07 18:36
(Received via mailing list)
On 07.06.2007 16:52, Peter Marsh wrote:
>> primes = Series.new(Starting_value,Some_block_to_define_serires)
>
> Just wanted to be a bit clearer about this, the second argument is a
> block which can generate nth term in a series. This would probally take
> a while for primes, but if it were recursive then it would be easier...

IMHO for a series it would be more natural to let the block calculate
a[n+1] from a[n] wouldn't it?  Of course, for Fibonacci this would only
work if you allow for multiple arguments.

Something like

#!ruby
class Serial
   include Enumerable

   def initialize(*init, &f)
     @init = init
     @f = f
   end

   def each(&b)
     a = b.arity
     current = @init
     loop do
       b[*current[0 ... a]]
       current = Array(@f[*current])
     end
     self
   end
end

s1 = Serial.new 0 do |x| x+1 end
s1.each {|x| p x; break if x > 10}

puts

s2 = Serial.new 0,1 do |a,b| [b,a+b] end
s2.each {|x| p x; break if x > 40}


Kind regards

  robert
703fbc991fd63e0e1db54dca9ea31b53?d=identicon&s=25 Robert Dober (Guest)
on 2007-06-07 21:43
(Received via mailing list)
On 6/7/07, Robert Klemme <shortcutter@googlemail.com> wrote:
>
>
>
> s1 = Serial.new 0 do |x| x+1 end
> s1.each {|x| p x; break if x > 10}
>
> puts
>
> s2 = Serial.new 0,1 do |a,b| [b,a+b] end
> s2.each {|x| p x; break if x > 40}
>

Robert I hope you do not mind my fantasy about/over/at??? your theme.

class Serial
  include Enumerable

  def initialize(*init, &f)
    @init = init
    @f = f
    @arity = f.arity
  end

  def get_some( some = nil, &b)
    @current = @init.dup
    if some && b.nil? then
      (0...some).inject([]) do |acc,|
        compute_next
        acc << @current.first
      end
    else
      a = b.arity
      loop do
        break if some && ( some -= 1 ) < 0
        b[*@current.first( a )]
        compute_next
      end
      self
    end
  end

  private
  def compute_next
    @current += Array( @f[*@current] )
    @current = @current.last @arity
  end
end

s1 = Serial.new 0 do |x| x+1 end
s1.get_some {|x| p x; break if x > 10}
puts "-"*42
puts s1.get_some(6)

puts "-"*42
f = Serial.new 1, 1 do |x, y| x + y end
f.get_some(6){ |x,| puts x }

puts "-"*42
a = Serial.new 1, 1, 1 do |x, y, z| x + y + z end
puts a.get_some(6)

Cheers
Robert
88c6023527fbe5a832d1092d7d032a95?d=identicon&s=25 fREW (Guest)
on 2007-06-07 22:19
(Received via mailing list)
On 6/7/07, Robert Dober <robert.dober@gmail.com> wrote:
> > work if you allow for multiple arguments.
> >    end
> > end
> Robert I hope you do not mind my fantasy about/over/at??? your theme.
>   def get_some( some = nil, &b)
>         b[*@current.first( a )]
>   end
>
> You see things; and you say Why?
> But I dream things that never were; and I say Why not?
> -- George Bernard Shaw
>
>

Isn't ruby cool?
E0d864d9677f3c1482a20152b7cac0e2?d=identicon&s=25 Robert Klemme (Guest)
on 2007-06-07 22:45
(Received via mailing list)
On 07.06.2007 21:41, Robert Dober wrote:
> On 6/7/07, Robert Klemme <shortcutter@googlemail.com> wrote:
>
> Robert I hope you do not mind my fantasy about/over/at??? your theme.

Not at all.  I had thought about the limit myself but did not want to
bother implementing it.  Two remarks about your code:

You include Enumerable but do not provide #each which is required.

You use instance variables for the iteration which is a bad thing
because this needless restricts usability (namely in the light of
multiple threads).  Array and other's also do not store the iteration
state in instance variables but in local variables in method #each.  You
can try it with something like this which would not work if instance
variables would be used for storing iteration state

a=(1..10).to_a
2.times {|i| Thread.new(i) {|j| a.each {|x| puts "[#{j}-#{x}]"; sleep
0.5}}}

Kind regards

  robert
703fbc991fd63e0e1db54dca9ea31b53?d=identicon&s=25 Robert Dober (Guest)
on 2007-06-07 23:13
(Received via mailing list)
On 6/7/07, Robert Klemme <shortcutter@googlemail.com> wrote:
> On 07.06.2007 21:41, Robert Dober wrote:
> > On 6/7/07, Robert Klemme <shortcutter@googlemail.com> wrote:
> >
> > Robert I hope you do not mind my fantasy about/over/at??? your theme.
>
> Not at all.  I had thought about the limit myself but did not want to
> bother implementing it.  Two remarks about your code:
>
> You include Enumerable but do not provide #each which is required.
Sure, bad error; that was a leftover of your code, I do not really
want to include it.
>
> You use instance variables for the iteration which is a bad thing
> because this needless restricts usability (namely in the light of
> multiple threads).
I am not sure I understand this point, but we can get rid of  that by
expanding compute_next, but this will make the code much less readable
:(
The whole beast is not thread safe at all I guess, even without the
instance var.

It would be a nice challenge to make it thread safe, I guess we would
need to cache values and synchronize the computation part, sounds
*very* expansive, time and memory wise; probably not worth it .
>Array and other's also do not store the iteration
> state in instance variables but in local variables in method #each.
Would that not be for performance reasons?
>  You
> can try it with something like this which would not work if instance
> variables would be used for storing iteration state
>
> a=(1..10).to_a
> 2.times {|i| Thread.new(i) {|j| a.each {|x| puts "[#{j}-#{x}]"; sleep 0.5}}}
I guess I do not know enough to understand this :(
How is concurrent access to the method not a problem with local
variables?
However it would be sufficient to synchronize the access to the method
only and not the access to the ivar. Is that what you are worried
about?

Cheers
Robert
6087a044557d6b59ab52e7dd20f94da8?d=identicon&s=25 Peña, Botp (Guest)
on 2007-06-08 04:47
(Received via mailing list)
On Behalf Of Peter Marsh:
# [2,6,18,54] series. So I suggest this:
# arithmetic_series = Arith.new(First_Term,Common_Difference)

nice, but i am poor in english, and there are too many words in ruby
already.
i'd propose extending Range a bit (i hope), like

Range.new(start, end, exclusive=false, diff=&:succ)

where diff could be
  &:succ where next term is succ
         this is the current implem
  &:pred where next term is pred (succ==pred)
         this has the effect of defining a reverse range
         ("z".."x")==("x".."z").reverse == Range.new("z".."x",,&:pred)
         "z".succ => "y"
         "y".succ => "x"
         eg, r=Range.new("z","x",,&:pred)
             r.each{|x| p x} => z y x
  &:+n   where next term is term+n
  &:-n   where next term is term-n
         eg, r=Range.new(100,96,,&:-2)
             r.each{|x| p x} => 100 98 96
  &:*n   where next term is term*n
  &:/n   where next term is term/n
  {blck} where {blck} is a code block
         where {block} defines next/succ
         eg, r=Range.new("0a","zz",) do |x|
                 case
                    when x=="0z"
                       "aa"
                 else
                    x.succ
                 end
               end
             r.each{|x| p x} => 0a 0b.. 0z aa ab ..yz zz

or something like that to that effect..
E0d864d9677f3c1482a20152b7cac0e2?d=identicon&s=25 Robert Klemme (Guest)
on 2007-06-08 12:25
(Received via mailing list)
On 07.06.2007 23:12, Robert Dober wrote:
> Sure, bad error; that was a leftover of your code, I do not really
> want to include it.
>>
>> You use instance variables for the iteration which is a bad thing
>> because this needless restricts usability (namely in the light of
>> multiple threads).
> I am not sure I understand this point, but we can get rid of  that by
> expanding compute_next, but this will make the code much less readable
> :(

You can as well add parameters and return values to compute_next.

> The whole beast is not thread safe at all I guess, even without the
> instance var.

Oh, it's perfectly thread safe if you change the use of instance
variables.

> It would be a nice challenge to make it thread safe, I guess we would
> need to cache values and synchronize the computation part, sounds
> *very* expansive, time and memory wise; probably not worth it .

Caching is only needed if you want to make it faster or more efficient.
  But for a general implementation I would not do it as it can have all
sorts of unwanted side effects.

>> Array and other's also do not store the iteration
>> state in instance variables but in local variables in method #each.
> Would that not be for performance reasons?

That's another advantage.

>>  You
>> can try it with something like this which would not work if instance
>> variables would be used for storing iteration state
>>
>> a=(1..10).to_a
>> 2.times {|i| Thread.new(i) {|j| a.each {|x| puts "[#{j}-#{x}]"; sleep
>> 0.5}}}
> I guess I do not know enough to understand this :(
> How is concurrent access to the method not a problem with local variables?

Because then there is iteration state per method invocation.  Compare
these two variants of #each:

class Foo
   # a must be an Array
   def initialize(a) @a=a.dup end

   # thread safe
   def each_1
     for i in 0...@a.size
       yield @a[i]
     end
     self
   end

   # not thread safe
   def each_2
     for @i in 0...@a.size
       yield @a[@i]
     end
     self
   end
end

Now, think about what happens if two threads invoke #each_1 and #each_2.

> However it would be sufficient to synchronize the access to the method
> only and not the access to the ivar.

That would work but it would limit usability - and there is no need to
do that.

Kind regards

  robert
703fbc991fd63e0e1db54dca9ea31b53?d=identicon&s=25 Robert Dober (Guest)
on 2007-06-08 14:28
(Received via mailing list)
On 6/8/07, Robert Klemme <shortcutter@googlemail.com> wrote:
> On 07.06.2007 23:12, Robert Dober wrote:
> > On 6/7/07, Robert Klemme <shortcutter@googlemail.com> wrote:
> >> On 07.06.2007 21:41, Robert Dober wrote:
> >> > On 6/7/07, Robert Klemme <shortcutter@googlemail.com> wrote:
> >> >

First of all thx for your time but I am not a quick learner :(

Obviously I am (or rather was )missing something very basic and if I
understand correctly that very basic is that method_invocations are on
copies of the local data, in each thread, is this *really* true? Well
you already showed with an example.

Hopefully I can put this into work tonight, gotta go back to work
here, hopefully this weeks Ruby Quiz will be boooring, please James ;)

Robert
E0d864d9677f3c1482a20152b7cac0e2?d=identicon&s=25 Robert Klemme (Guest)
on 2007-06-08 15:16
(Received via mailing list)
On 08.06.2007 14:27, Robert Dober wrote:
> understand correctly that very basic is that method_invocations are on
> copies of the local data, in each thread, is this *really* true? Well
> you already showed with an example.

Even more fine granular: there is one copy of local variables /per
invocation/ of a method.  You can play a bit with this to see the
effect:

def recurse(i = 5)
   s = "#{Thread.current.inspect} #{i} "
   print s, "enter\n"
   recurse(i - 1) if i > 0
   print s, "leave\n"
end

If you then do something like

2.times { Thread.new { recurse } }

You'll notice how values for "enter" decrease nicely and increase for
"leave" per thread.  Internally Ruby has a stack that stores all local
variables (including method arguments) and every time a method is
invoked a new stack frame is put on the stack which stores all those
values.  This is basically how most popular programming languages work.

> Hopefully I can put this into work tonight, gotta go back to work
> here, hopefully this weeks Ruby Quiz will be boooring, please James ;)

:-)

Kind regards

  robert
703fbc991fd63e0e1db54dca9ea31b53?d=identicon&s=25 Robert Dober (Guest)
on 2007-06-08 22:08
(Received via mailing list)
On 6/8/07, Robert Klemme <shortcutter@googlemail.com> wrote:
> On 08.06.2007 14:27, Robert Dober wrote:
> > On 6/8/07, Robert Klemme <shortcutter@googlemail.com> wrote:
> >> On 07.06.2007 23:12, Robert Dober wrote:
> >> > On 6/7/07, Robert Klemme <shortcutter@googlemail.com> wrote:
> >> >> On 07.06.2007 21:41, Robert Dober wrote:
> >> >> > On 6/7/07, Robert Klemme <shortcutter@googlemail.com> wrote:
That's a dialog, right, I wonder if OP lost interest or did I just
hitchhike another thread?

let us see what I came up with under your tutorship.

require 'test/unit'
class Serial

  def initialize(*init, &f)
    @init = init
    @f = f
    @arity = f.arity
  end

  def get_some( some = nil, &b)
    current = @init.dup
    if some && b.nil? then
      r = @init.dup
      (some - r.size).times do
        current = compute_next( current )
        r << current.last
      end
      r
    else
      a = b.arity
      loop do
        break if some && ( some -= 1 ) < 0
        b[ *current.first( a ) ]
        current = compute_next( current )
      end
      self
    end
  end

  private
  def compute_next current
    (current + Array( @f[*current] ) ).last @arity
  end
end
if __FILE__ == $0 then

  class Testee < Test::Unit::TestCase
    def test_1
      s1 = Serial.new 0 do |x| x+1 end
      assert_equal [*0..3], s1.get_some( 4 )
      a = []
      s1.get_some{ |x| a  << x; break if x > 10 }
      assert_equal [*0..11], a
    end # def test_1

    def test_2
      f = Serial.new 1, 1 do |x, y| x + y end
      assert_equal [1,1,2,3,5,8], f.get_some(6)
      a = []
      f.get_some{ |x| a  << x; break if x > 10 }
      assert_equal [1,1,2,3,5,8,13], a
      a = []
      f.get_some(4){ |x| a.unshift x }
      assert_equal [3,2,1,1], a
    end # def test_2


    def test_3
      f = Serial.new 0, 0, 1 do |a, b, c| 3*a + 2*b + c end
      assert_equal [0,0,1,1,3,8,17,42,100], f.get_some(9)
    end # def test_3
  end # class Testee < Test::Unit::TestCase
end

Thanks again

Robert
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