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comp.lang.ruby

The Challenge of R

T. Onoma

10/13/2004 4:47:00 AM

Here's a coding challenge you.

The R language has the following nifty features for working with arrays. To
what degree can you get Ruby to do the same?

The solution that is closest/nicest gets forever embedded in my growing
library of Ruby enhancements, and it's author's name wrapped in shiny
asterisks and number signs! Joy, joy! :)


Listing 1. Elementwise operations in R

> a = 1:10 # Range of numbers 1 through 10
> b = a+5 # Add 5 to each element
> b # Show b vector
[1] 6 7 8 9 10 11 12 13 14 15

Or you can operate selectively only on elements with certain indices, by using
an "index array":


Listing 2. Using index arrays to select elements

> c = b # Make a (lazy) copy of b
> pos = c(1,2,3,5,7) # Change the prime indices
> c[pos] = c[pos]*10 # Reassign to indexed positions
> c # Show c vector
[1] 60 70 80 9 100 11 120 13 14 15

Or, maybe best of all, you can use a syntax much akin to list comprehensions
in Haskell or Python, and only operate on elements that have a desired
property:


Listing 3. Using predicates to select elements

> d = c
> d[d %% 2 == 0] = -1 # Reassign -1 to all even elements
> d
[1] -1 -1 -1 9 -1 11 -1 13 -1 15


---

Note, I've gotten pretty far on my own solution, but can't seem to get passed
a certain point --the Functor class I presented a week or so ago has proven
useful.

Finally special thanks to Martin DeMello who got me hell bent on this ;)

T.
10 Answers

gabriele renzi

10/13/2004 7:59:00 AM

0

trans. (T. Onoma) ha scritto:

> Here's a coding challenge you.
>
> The R language has the following nifty features for working with arrays. To
> what degree can you get Ruby to do the same?

Interesting to see people playing with array programming in ruby..
Sometimes I wish I had F-Script like array operations..

btw, nothing ot say about this problem, but notice that there is access
to the R library from ruby: http://raa.ruby-lang.org/project/ruby...

Ara.T.Howard

10/13/2004 8:15:00 AM

0

Niklas Frykholm

10/13/2004 8:24:00 AM

0

trans. (T. Onoma) wrote:
> Here's a coding challenge you.
>
> The R language has the following nifty features for working with arrays. To
> what degree can you get Ruby to do the same?

Here's my take. I haven't wrapped it up in a nice module, but it solves
the sample problems you gave:


class Elements
include Enumerable

attr_reader :array

def initialize(array, indices = nil)
@array = array
@indices = indices
@indices = (0...@array.size).to_a unless @indices
end

def method_missing(symbol, *args)
res = []
@indices.each {|i|
res << @array[i].send(symbol, *args)
}
return Elements.new(res)
end

def to_s
res = ""
@indices.each {|i|
res << @array[i].to_s << " "
}
return res
end

def indices(x)
res = []
if x.respond_to?(:call)
@indices.each {|i| res << i if x.call(@array[i])}
elsif x.respond_to?(:each)
x.each {|i| res << @indices[i] }
else
res << x
end
return res
end

def [] (x)
return Elements.new(@array, indices(x))
end

def []= (x,y)
ind = indices(x)
if y.respond_to?(:each_with_index)
y.each_with_index {|v, i| @array[ ind[i] ] = v }
else
ind.each {|i| @array[i] = y}
end
end

def each
@indices.each {|i| yield @array[i]}
end
end

class Array
def elements
return Elements.new(self)
end
end

a = (1..10).to_a
a = a.elements

b = a + 5
puts b

c = b
pos = [0, 1, 2, 4, 6]
c[pos] = c[pos] * 10
puts c

d = c
d[ proc {|x| x % 2 == 0} ] = -1
puts d

T. Onoma

10/13/2004 2:09:00 PM

0

On Wednesday 13 October 2004 03:59 am, gabriele renzi wrote:
| trans. (T. Onoma) ha scritto:
| > Here's a coding challenge you.
| >
| > The R language has the following nifty features for working with arrays.
| > To what degree can you get Ruby to do the same?
|
| Interesting to see people playing with array programming in ruby..
| Sometimes I wish I had F-Script like array operations..

Care to elaborate?

| btw, nothing ot say about this problem, but notice that there is access
| to the R library from ruby: http://raa.ruby-lang.org/project/ruby...

And I discovered R for Ruby! Nice.

Thanks,
T.

T. Onoma

10/13/2004 2:13:00 PM

0

On Wednesday 13 October 2004 04:24 am, Ara.T.Howard@noaa.gov wrote:
| i did not write it, but narray does all that you want, and more, including
| being extremely fast, doing simply display of data in X, and working
| seamlessly with memory mapping:

I did not know NArray worked elementwise. Nice. For numbers at least, that's
one hell of a solution Ara ;)

| jib:~ > cat a.rb
| require 'narray'
|
| a = NArray[1..10]
| b = a + 5
| p b
|
| c = b
| pos = 0,1,2,4,6 # adjust R's 1 based idx to ruby's 0 based
| c[pos] = c[pos] * 10
| p c
|
| d = c
| d[(d % 2).eq(0).where] = -1
| p d
|
| jib:~ > ruby a.rb
| NArray.int(10):
| [ 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 ]
| NArray.int(10):
| [ 60, 70, 80, 9, 100, 11, 120, 13, 14, 15 ]
| NArray.int(10):
| [ -1, -1, -1, 9, -1, 11, -1, 13, -1, 15 ]
|
| you can thank Masahiro Tanaka for such a great work.
|
| http://www.ir.isas.ac.jp/~masa/ruby/in...

Double thanks!

T.

Ara.T.Howard

10/13/2004 3:53:00 PM

0

T. Onoma

10/13/2004 5:00:00 PM

0

On Wednesday 13 October 2004 12:05 pm, Ara.T.Howard@noaa.gov wrote:
| On Wed, 13 Oct 2004, trans. (T. Onoma) wrote:
| > I did not know NArray worked elementwise. Nice. For numbers at least,
| > that's one hell of a solution Ara ;)
|
| it also works with any objects:
|
| jib:~ > cat b.rb
| require 'narray'
| na = NArray::to_na ['4', '7', '9', '2']
| puts(na[(na < '5').where].to_a.join)
|
| jib:~ > ruby b.rb
| 42

Oh, even better. Then what does N stand for? I thought it was Numeric.

Moreover, what are the important differences between Array and NArray. Why
does Ruby choose Array over NArray?

Thanks,
T.

gabriele renzi

10/13/2004 10:39:00 PM

0

trans. (T. Onoma) ha scritto:

> On Wednesday 13 October 2004 03:59 am, gabriele renzi wrote:
> | trans. (T. Onoma) ha scritto:
> | > Here's a coding challenge you.
> | >
> | > The R language has the following nifty features for working with arrays.
> | > To what degree can you get Ruby to do the same?
> |
> | Interesting to see people playing with array programming in ruby..
> | Sometimes I wish I had F-Script like array operations..
>
> Care to elaborate?
>

you can read what I mean here (better than what I can explain):
http://www.fscript.org/download...

maybe on ruby-suby there is space for some debate about it, but notice
that I just said "sometimes" ;)

T. Onoma

10/14/2004 2:53:00 AM

0

On Wednesday 13 October 2004 06:39 pm, gabriele renzi wrote:
| trans. (T. Onoma) ha scritto:
| > On Wednesday 13 October 2004 03:59 am, gabriele renzi wrote:
| > | trans. (T. Onoma) ha scritto:
| > | > Here's a coding challenge you.
| > | >
| > | > The R language has the following nifty features for working with
| > | > arrays. To what degree can you get Ruby to do the same?
| > |
| > | Interesting to see people playing with array programming in ruby..
| > | Sometimes I wish I had F-Script like array operations..
| >
| > Care to elaborate?
|
| you can read what I mean here (better than what I can explain):
| http://www.fscript.org/download...
|
| maybe on ruby-suby there is space for some debate about it, but notice
| that I just said "sometimes" ;)

Debate? Don't think so. It's suby-ruby, btw.

Thanks for the link though. I'll have a look.
T.

T. Onoma

10/15/2004 5:00:00 PM

0

Niklas,

I'm still working on how to incorporate your code into my lib, but you get the
glorious prize ;) Here's your star spangled banner!

#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#
# SPECIAL THANKS TO #
#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#
# #
# * * * Niklas Frykholm * * * #
# * * * #
# * * * #
# * #
# #
#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#

Nice work!
T.