# N-dimensional array in Ruby

**URL:** <https://www.ruby-forum.com/t/n-dimensional-array-in-ruby/152265>\
**Category:** Ruby\
**Created:** [November 1, 2008, 1:10am UTC](https://www.ruby-forum.com/t/n-dimensional-array-in-ruby/152265 "2008-11-01T01:10:57Z")\
**Posts on this page:** 7\
**Page:** 1

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**Author:** ![christian](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/b2d939/32.png) [@christian](https://www.ruby-forum.com/u/christian)\
**Post date:** [November 1, 2008, 1:10am UTC](https://www.ruby-forum.com/t/n-dimensional-array-in-ruby/152265/1 "2008-11-01T01:10:57Z")

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Hi,

i have a little Java problem, I want to solve using Ruby. Therefor I  
need an n-dimensional array. In Java it looks like this:

double dArray[][][] = new double[x.length()+1][y.length()+1][x.length()  
+y.length()+3];  
dArray[0][0][0] = 0;  
dArray[0][0][1] = POSITIVE\_INFINITY;

Further values will be computed through loops and written into the  
array.

How do I initialize such an array in Ruby?

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<div class="post-metadata">

**Author:** ![christian](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/b2d939/32.png) [@christian](https://www.ruby-forum.com/u/christian)\
**Post date:** [November 1, 2008, 1:31am UTC](https://www.ruby-forum.com/t/n-dimensional-array-in-ruby/152265/2 "2008-11-01T01:31:25Z")

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On Fri, Oct 31, 2008 at 8:09 PM, Christian [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)  
wrote:

> Further values will be computed through loops and written into the  
> array.
> 
> How do I initialize such an array in Ruby?

Infinity = 1.0/0

a = [[],[],[]]  
a[0][0][0] = 0  
a[0][0][1] = Infinity

The arrays will grow to whatever size you need them to.

HTH,  
Michael G.

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<div class="post-metadata">

**Author:** ![christian](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/b2d939/32.png) [@christian](https://www.ruby-forum.com/u/christian)\
**Post date:** [November 1, 2008, 1:46am UTC](https://www.ruby-forum.com/t/n-dimensional-array-in-ruby/152265/3 "2008-11-01T01:46:31Z")

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Christian wrote:

> i have a little Java problem, I want to solve using Ruby. Therefor I  
> need an n-dimensional array.

def Array.multi(\*dimensions)  
dimensions.reverse.inject(nil) { |result, dim|  
Array.new(dim) { result ? result.dup : nil }  
}  
end

a = Array.multi(3, 4, 5)

p a[0] #=\> [[nil, nil, …], … ]  
p a[0][0] #=\> [nil, nil, nil, nil, nil]

a[0][0][0] = :fred  
a[2][3][4] = :barney

p a[0][0][0] #=\> :fred  
p a[2][3][4] #=\> :barney

a[3][0][0]

# =\> exception: undefined method `[]’ for nil; index past dim size

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<div class="post-metadata">

**Author:** ![christian](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/b2d939/32.png) [@christian](https://www.ruby-forum.com/u/christian)\
**Post date:** [November 1, 2008, 5:45pm UTC](https://www.ruby-forum.com/t/n-dimensional-array-in-ruby/152265/4 "2008-11-01T17:45:36Z")

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Mike G. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) writes:

> dimensions.reverse.inject(nil) { |result, dim|  
> Array.new(dim) { Marshal.load(Marshal.dump(result)) }  
> }  
> end

Yearning for macros…

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<div class="post-metadata">

**Author:** ![christian](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/b2d939/32.png) [@christian](https://www.ruby-forum.com/u/christian)\
**Post date:** [November 1, 2008, 10:05am UTC](https://www.ruby-forum.com/t/n-dimensional-array-in-ruby/152265/5 "2008-11-01T10:05:13Z")

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Mike G. wrote:

> def Array.multi(\*dimensions)  
> dimensions.reverse.inject(nil) { |result, dim|  
> Array.new(dim) { result ? result.dup : nil }  
> }  
> end

My mistake. Array#dup is not a recursive deep copy.

def Array.multi(\*dimensions)  
dimensions.reverse.inject(nil) { |result, dim|  
Array.new(dim) { Marshal.load(Marshal.dump(result)) }  
}  
end

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<div class="post-metadata">

**Author:** ![christian](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/b2d939/32.png) [@christian](https://www.ruby-forum.com/u/christian)\
**Post date:** [November 1, 2008, 5:46pm UTC](https://www.ruby-forum.com/t/n-dimensional-array-in-ruby/152265/6 "2008-11-01T17:46:11Z")

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Michael G. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) writes:

> > Further values will be computed through loops and written into the  
> > array.
> > 
> > How do I initialize such an array in Ruby?
> 
> Infinity = 1.0/0

~$ irb  
irb(main):001:0\> X = 7  
=\> 7  
irb(main):002:0\> Infinity = 1.0/0  
=\> Infinity  
irb(main):003:0\> 0 / Infinity  
=\> 0.0  
irb(main):004:0\> Infinity \* Infinity  
=\> Infinity  
irb(main):005:0\> Beyond = Infinity  
=\> Infinity  
irb(main):006:0\> 2 \* Infinity and Beyond  
=\> Infinity  
irb(main):007:0\> Infinity.infinite?  
=\> 1

Cool - I just learned about Infinity in Ruby. Hey Dave T., maybe  
you could add a bit about Infinity in the next relase of Programming  
Ruby or Programming Ruby 1.9

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<div class="post-metadata">

**Author:** ![christian](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/b2d939/32.png) [@christian](https://www.ruby-forum.com/u/christian)\
**Post date:** [November 1, 2008, 6:04pm UTC](https://www.ruby-forum.com/t/n-dimensional-array-in-ruby/152265/7 "2008-11-01T18:04:55Z")

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On Sat, Nov 1, 2008 at 12:43 PM, Brian A. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)  
wrote:

> > > dArray[0][0][0] = 0;  
> > > irb(main):001:0\> X = 7  
> > > =\> Infinity  
> > > irb(main):007:0\> Infinity.infinite?  
> > > =\> 1
> 
> Cool - I just learned about Infinity in Ruby. Hey Dave T., maybe  
> you could add a bit about Infinity in the next relase of Programming  
> Ruby or Programming Ruby 1.9

Yeah, I don’t think I’ve seen it discussed in any books before, but I  
could be wrong.

I stumbled upon it accidentally one day when playing with ruby and  
it’s rules for division.

Michael G.