Two Dimensional Arrays in Ruby?

No doubt this question has been asked before but I cannot find it and it
is
not documented in three Ruby books I’ve checked, which is very strange
as
two dimensional arrays are a common need in programming.

How does one define and use a two dimensional array in Ruby?

I tried
anarray = [[1, 2, 3], [4, 5, 6] [7, 8, 9]]
with
puts anarray[1][1]
does not deliver the 5 that I would expect but instead, provides (in
SciTE)
the error message on the line defining the array:

ruby test_2_dimensional_array.rb
test_2_dimensional_array.rb:1:in `[]’: wrong number of arguments (3 for

(ArgumentError)
from test_2_dimensional_array.rb:1

Exit code: 1

So what is the secret for working with two dimensional arrays in Ruby?
And
is it documented somewhere?

Thanks in advance!

Mason K. wrote:

So what is the secret for working with two dimensional arrays in Ruby?
And
is it documented somewhere?

Thanks in advance!

Maybe you should call on your 20 years of computer programming
experience in 30 different languages to do a little debugging:

anarray = [
[1, 2, 3],
[4, 5, 6],
[7, 8, 9]
]
puts anarray[1][1]

–output:–
5

Mon, Sep 7, 2009 at 12:11 PM, Mason K. [email protected] wrote:

anarray = [[1, 2, 3], [4, 5, 6] [7, 8, 9]]
puts anarray[1][1]

Try adding a comma between the second and third array. :slight_smile:
anarray = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]

Harry

Mason K. wrote:

And
is it documented somewhere?

Oh, yeah. If you look up Arrays in the index of your book, on one of
the pages you will find something like this:


However, in Ruby specifically, arrays are ordered collection of objects.
[B]ecause everything in Ruby is an object[,] [a]rrays can contain any
combination of objects of any class.

p. 574 Beginning Ruby: From Novice to Professional

On Sun, Sep 6, 2009 at 10:11 PM, Mason K. [email protected]
wrote:

does not deliver the 5 that I would expect but instead, provides (in SciTE)
Thanks in advance!

Hi, Mason

In Ruby, Arrays are objects, they only have one dimension. But they can
hold
anything, including other arrays, so they can behave as multi
dimensional
arrays. To get your desired output, you would so something like this

#a two dimensional array
x = Array.new(3){ Array.new(3) }
p x # => [[nil, nil, nil], [nil, nil, nil], [nil, nil, nil]]

#a two dimensional array with your desired output
x = Array.new(3){|i| Array.new(3){|j| 3*i+j+1 } }
x # => [[1, 2, 3], [4, 5, 6], [7, 8, 9]]

In this example, we say Array.new(3) which says to make an array with
three
indexes. Then we pass it a block, which determines how to initialize
each
index. The block accepts the variable i, which is the index being
assigned,
so it will have values 0, 1, and 2. Then for each of these indexes, we
want
it to be an Array, which gets us our second dimension. So in our block
we
assign another Array.new(3), to say an array with three indexes. We pass
this Array the block {|j| 3*i+j+1} so j will have values 0, 1, 2 and i
will
have values 0, 1, 2. Then we multiply i by 3, because each second
dimension
has three indexes, and we add 1 because we want to begin counting at 1
instead of zero.

So this says “create an array with three indexes, where each index is an
array with three indexes, whose values are 3 times the index of the 1st
dimension, plus the second dimension, plus 1”

Hope that helps.

Your helpfulness is appreciated. Unfortunately at age 68 my eyesight is
not
what it used to be. It works fine when I insert to missing comma. Ah!
Programming is a young person’s game.

anarray = [[1, 2, 3], [4, 5, 6], [7, 8, 0]]
puts anarray[1][1]
puts anarray[0]
puts anarray[2][0]

produces (SciTE)

ruby test_2_dimensional_array.rb
5
1
2
3
7
Exit code: 0

I’m writing a move method for the 8-puzzle problem for my artificial
intelligence class and need a two dimensional way of representing the
positions of the tiles.

Again, thanks.

No Sam

2009/9/7 Mason K. [email protected]:

positions of the tiles.
You don’t have to do this low level. After all, Ruby is an OO
language. You can use class Matrix:

$ irb19 -r matrix
Ruby version 1.9.1
irb(main):001:0> m = Matrix[[1, 2, 3], [4, 5, 6], [7, 8, 0]]
=> Matrix[[1, 2, 3], [4, 5, 6], [7, 8, 0]]
irb(main):002:0> m[1,1]
=> 5
irb(main):003:0>

Cheers

robert

7stud, you need not be jealous of my experience. Yes, I have learned
over
100 languages and had a career of 36 years as a programmer. But only a
few
of the languages I learned are still viable. Computer languages are
dime a
dozen and knowledge of them has a funny way of becoming irrelevant. And
age
(I’m 68) does have its own clever ways of leveling the playing field.
My
eyesight was not good enough to catch such a trivial error. If I am
fortunate, then, I have helped you debug the problem you have. I wish
you
the best and hope you will use your talents wisely.

No Sam

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