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comp.lang.ruby

a deepcopy for "array = [1,2,3]*5"?

Ardanwen

5/23/2005 12:18:00 PM

Been looking this up in the myriad of deepcopy strands, but couldn't
find it in 30 minutes, so I'm posting the question.

The question is simple. What way would you create an array that
contains 5 copies of an array, without the copies interfering with each
other?

array = [1,2,3]*5

generates:
[[1,2,3],[1,2,3],[1,2,3],[1,2,3],[1,2,3]]

but unfortunately also makes 'array[1][1] = "a"' change it like this:

[[1,"a",3],[1,"a",3],[1,"a",3],[1,"a",3],[1,"a",3]]

---------
Anyway, found a solution during tinkering, although I don't know why.
Thought I'd just still post it anyway.

ar = []
5.times{ar << [1,2,3]}

works, and 'array[1][1] = "a"' results in the thing I want

[[1,2,3],[1,"a",3],[1,2,3],[1,2,3],[1,2,3]]
3 Answers

Florian Frank

5/23/2005 12:28:00 PM

0

On 2005-05-23 21:20:17 +0900, Boris wrote:
> The question is simple. What way would you create an array that
> contains 5 copies of an array, without the copies interfering with each
> other?

array = Array.new(5) { [1,2,3] }

--
Florian Frank

Brian Schröder

5/23/2005 12:29:00 PM

0

On 23/05/05, Boris <bvschmid@gmail.com> wrote:
> Been looking this up in the myriad of deepcopy strands, but couldn't
> find it in 30 minutes, so I'm posting the question.
>
> The question is simple. What way would you create an array that
> contains 5 copies of an array, without the copies interfering with each
> other?
>
> array = [1,2,3]*5
>
> generates:
> [[1,2,3],[1,2,3],[1,2,3],[1,2,3],[1,2,3]]
>
> but unfortunately also makes 'array[1][1] = "a"' change it like this:
>
> [[1,"a",3],[1,"a",3],[1,"a",3],[1,"a",3],[1,"a",3]]
>
> ---------
> Anyway, found a solution during tinkering, although I don't know why.
> Thought I'd just still post it anyway.
>
> ar = []
> 5.times{ar << [1,2,3]}
>
> works, and 'array[1][1] = "a"' results in the thing I want
>
> [[1,2,3],[1,"a",3],[1,2,3],[1,2,3],[1,2,3]]
>
>

For me [1,2,3]*5 behaves different.

irb(main):001:0> [1,2,3]*5
=> [1, 2, 3, 1, 2, 3, 1, 2, 3, 1, 2, 3, 1, 2, 3]


For what you want you could use:

irb(main):002:0> a = Array.new(5) { [1,2,3] }
=> [[1, 2, 3], [1, 2, 3], [1, 2, 3], [1, 2, 3], [1, 2, 3]]
irb(main):003:0> a[1][1] = 'a'
=> "a"
irb(main):004:0> a
=> [[1, 2, 3], [1, "a", 3], [1, 2, 3], [1, 2, 3], [1, 2, 3]]

$ ruby -v
ruby 1.8.2 (2005-04-11) [i386-linux]

Which version of ruby are you using?

best regards,

Brian Schröder

--
http://ruby.brian-sch...

Stringed instrument chords: http://chordlist.brian-sch...

Premshree Pillai

5/23/2005 2:59:00 PM

0

On 5/23/05, Brian Schröder <ruby.brian@gmail.com> wrote:
> For me [1,2,3]*5 behaves different.
>
> irb(main):001:0> [1,2,3]*5
> => [1, 2, 3, 1, 2, 3, 1, 2, 3, 1, 2, 3, 1, 2, 3]

He prolly meant [[1, 2, 3]]*5

--
Premshree Pillai