How to copy array in ruby

Ruby
1

HI

I am a novice in Ruby programming so this question might look trivial
to lot of people.

But I am struggling to copy an array.

I am using

a = []
b = a

/* some manipulation here on “b” and “a” I havent touched at all*/

Here when i am trying to see contents of “a” and “b” both have same
contents

But my expectation was they shud be different

Instead of b = a, I also tried b.replace(a)

but no luck here also.

Please help me on how to make a duplicate(“b”) of “a” so that changes
done on b will not affect a

Thanks
Pikender Sharma

2

On Fri, Nov 13, 2009 at 2:30 PM, PIKI [email protected] wrote:

contents

But my expectation was they shud be different

Instead of b = a, I also tried b.replace(a)

but no luck here also.

Please help me on how to make a duplicate(“b”) of “a” so that changes
done on b will not affect a

irb(main):001:0> a = [1,2,3,4]
=> [1, 2, 3, 4]
irb(main):002:0> b = a.dup
=> [1, 2, 3, 4]
irb(main):003:0> b[0] = 55
=> 55
irb(main):004:0> a
=> [1, 2, 3, 4]
irb(main):005:0> b
=> [55, 2, 3, 4]

Hope this helps,

Jesus.

3

On Nov 13, 6:34 pm, Jesús Gabriel y Galán [email protected]
wrote:

Here when i am trying to see contents of “a” and “b” both have same

Hope this helps,

Jesus.- Hide quoted text -

  • Show quoted text -

Hi Jesús Gabriel y
Galán
Thanks for the reply and help

I tried ur solution but it is also not working :frowning:

I am unable to figure out the trick

Thanks
Pikender Sharma

4

I tried ur solution but it is also not working :frowning:

I am unable to figure out the trick

In order to help us to figure out what is the problem, you might want
to post a code snippet demonstrating the defect and explain what how
you would expect ruby to behave.

Array#dup creates a copy of the array, not of the elements in the
array, aka a shallow copy.

5

l> Array#dup creates a copy of the array, not of the elements in the
l> array, aka a shallow copy.

Is there a way to make a deep copy? That is … in the code below,
could b.dup be replaced with something like b.deepdup?

irb(main):019:0> a1 = [1,2,3,4]
=> [1, 2, 3, 4]
irb(main):020:0> b = [a1,5]
=> [[1, 2, 3, 4], 5]
irb(main):021:0> c1 = b
=> [[1, 2, 3, 4], 5]
irb(main):022:0> c2 = b.dup
=> [[1, 2, 3, 4], 5]
irb(main):023:0> a1[0] = “hi”
=> “hi”
irb(main):024:0> a1
=> [“hi”, 2, 3, 4]
irb(main):025:0> c1
=> [[“hi”, 2, 3, 4], 5]
irb(main):026:0> c2

because of the shallow copy, c2[0][0] is “hi” instead of a naively

assumed 1.

=> [[“hi”, 2, 3, 4], 5]
irb(main):027:0> c1[1] = “bye”
=> “bye”
irb(main):028:0> c1
=> [[“hi”, 2, 3, 4], “bye”]
irb(main):029:0> c2

The shallow copy gives the expected result for c2[1], below.

=> [[“hi”, 2, 3, 4], 5]

6

Ralph S.:

Is there a way to make a deep copy? That is … in the code
below, could b.dup be replaced with something like b.deepdup?

If the contents of the array are marshalable, you can
try the idiomatic Marshal.dump/Marshal.load cycle:

array = [[:a1, :a2], :b]
=> [[:a1, :a2], :b]

dup = array.dup
=> [[:a1, :a2], :b]

dup[0] << :a3
=> [:a1, :a2, :a3]

dup
=> [[:a1, :a2, :a3], :b]

array
=> [[:a1, :a2, :a3], :b]

deep = Marshal.load Marshal.dump(array)
=> [[:a1, :a2, :a3], :b]

deep[0] << :a4
=> [:a1, :a2, :a3, :a4]

deep
=> [[:a1, :a2, :a3, :a4], :b]

array
=> [[:a1, :a2, :a3], :b]

— Shot

7

you can make it via this method “clone” b = a.clone
Am 14.11.2009 um 11:25 schrieb PIKI: