Ruby copy an array of arrays

Question

Is there a way in Ruby to make a copy of multi-dimensional array? I mean some built-in function.

When I try to use .dup it just returns reference:

irb(main):001:0> a = [[1,2,3], [4,5,6]]
=> [[1, 2, 3], [4, 5, 6]]
irb(main):002:0> b = a.dup
=> [[1, 2, 3], [4, 5, 6]]
irb(main):003:0> b[0][0] = 15
=> 15
irb(main):004:0> a == b
=> true

Sionide21 · Accepted Answer · 2012-05-09 11:48:12Z

15

You need to dup the arrays in the list instead of just the outer one. The easiest way is probably something like

b = a.map(&:dup)

answered May 9, 2012 at 11:48

Sionide21

2,2113 gold badges21 silver badges30 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

jgomo3 Over a year ago

I suppose this only works for 1 extra dimension. What about N-dimensions? I suppose dup should be applied recursively on each object.

dexter · Accepted Answer · 2012-05-09 11:14:18Z

8

Marshaling should do the trick:

jruby-1.6.7 :001 > a = [[1,2,3], [4,5,6]]
 => [[1, 2, 3], [4, 5, 6]] 
jruby-1.6.7 :002 > b = Marshal.load( Marshal.dump(a) )
 => [[1, 2, 3], [4, 5, 6]] 
jruby-1.6.7 :004 > a == b
 => true 
jruby-1.6.7 :005 > b[0][0] = 15
 => 15 
jruby-1.6.7 :006 > a == b
 => false

answered May 9, 2012 at 11:14

dexter

13.6k5 gold badges42 silver badges56 bronze badges

Collectives™ on Stack Overflow

Ruby copy an array of arrays

2 Answers 2

1 Comment

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Related