Matrix-element extractor -- How to define it

Ruby
1

Hi,

I defined and populated a 9x9 matrix (Array of Arrays) of strings, m

I defined an element-extractor:

class Array
def get(i,j)
line =self[i-1]
char = line[j-1]
end
end

To get the first element of the second row, I used the following,
which worked fine:

m.get(2,1)

I’d like to write merely m(2,1). How can I do that simply?

Thanks in Advance,
Richard

2

Hi,

You do this:
class Array
alias old_[] []
def [] *args
if *args.length == 2 && args[0].is_a? Integer && args[1].is_a?
Integer
get(*args)
else
old_
end
end

Of course, this would remove some of the functionality of an Array for
every Array, not just matricies. Consider making a subclass of Array
like this:
class Matrix < Array
…
end

Now you can modify Matrix at will without affecting Array.

If you are creating a Matrix for purely pragmatic reasons (i.e., not
as an excercise) then there is an excellent Matrix class in the Ruby
standard library: RDoc Documentation

Dan

On Sat, May 3, 2008 at 4:05 PM, RichardOnRails

3

On May 3, 9:06 pm, Daniel F. [email protected] wrote:

end

To get the first element of the second row, I used the following,
which worked fine:

m.get(2,1)

I’d like to write merely m(2,1). How can I do that simply?

Thanks in Advance,
Richard

Hi Daniel,

Thanks for the “kick start” and the Matrix class. I got the latter
working, but I’m going to “roll my own” because I want a Sudoku
solver that works the way I do manually. I know there’s a free solver
written in VisualProlog, but like Frank Sinatra, “I’ll do it my
way” :slight_smile:

alias old_[] []

I’m running ruby 1.8.6 (2007-09-24 patchlevel 111) [i386-mswin32]. It
barfed on “old_”, so I substituted:
else
super(*args)
which worked fine.

Best wishes,
Richard

4

On May 4, 4:38 pm, RichardOnRails
[email protected] wrote:

if *args.length == 2 && args[0].is_a? Integer && args[1].is_a? Integer

…
On Sat, May 3, 2008 at 4:05 PM, RichardOnRails

            line =self[i-1]

alias old_[] []

I’m running ruby 1.8.6 (2007-09-24 patchlevel 111) [i386-mswin32]. It
barfed on “old_”, so I substituted:
else
super(*args)
which worked fine.

Best wishes,
Richard

I should have mentioned that I used "alias old_[] [] " in the context
of “Matrix < Array”, so there’s no wonder it didn’t work. Sorry about
that omission.

5

Hi again,

I’m glad super worked out for you. That’s the “right way” to do it
for inheritance.

I have a feeling I may have misguided you with the “alias old_[] []”
line. It should probably be something like “alias old_brackets []” as
I doubt that old_[] is a valid method name (I just checked and it
isn’t, to be sure).

Dan

On Sun, May 4, 2008 at 4:40 PM, RichardOnRails

6

On May 4, 5:44 pm, Daniel F. [email protected] wrote:

Dan

def [] *args
class Matrix < Array

    def get(i,j)

I’d like to write merely m(2,1). How can I do that simply?
way" :slight_smile:
Richard
Hi Daniel,

Thanks for your additional response.

misguided

No problem! I misguide myself all the time :slight_smile: Any, it’s history.

I’ve got two questions about my current version of your code, which
works fine BTW.

  1. Where is the get method come from. I looked in Ruby RDoc and (i)
    see no get method for Array, nor (ii) any related get method on the
    Methods section of the RDoc. I’d really like a pointer to it’s
    documentation. It certainly is useful in this context.

  2. As I mentioned, I switched from “old_” in the else
    clause to “super *args”. which works fine for the most part. I works
    fine, too, except I want to substitute “raise ‘invalid data’” or
    something more descriptive. Unfortunately, when I do that I get a
    syntax error.

If you have the time, I’d love to get your take on these issues.
Code and output is below for your convenience.

Best wishes,
Richard

class Matrix < Array
def [] *args
if (args.length == 2) && args[0].is_a?(Integer) && args[1].is_a?
(Integer)
get(*args)
else
super *args
end
end
end

m = Matrix[ [10,20,30], [40,50,60], [70,80,90] ];
puts m [0] [1] # 20
puts m [2] [0] # 70
puts m[1] # 40
# 50
# 60

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