# How do arrays in Ruby work? **URL:** \ **Category:** Ruby\ **Created:** [March 14, 2009, 3:14pm UTC](https://www.ruby-forum.com/t/how-do-arrays-in-ruby-work/162851 "2009-03-14T15:14:54Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![woodzer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/f08c70/32.png) [@woodzer](https://www.ruby-forum.com/u/woodzer)\ **Post date:** [March 14, 2009, 3:14pm UTC](https://www.ruby-forum.com/t/how-do-arrays-in-ruby-work/162851/1 "2009-03-14T15:14:54Z")
As in how they are organized behind the scenes. For example, if I say arr = [1, 2, 3, 4] arr.slice[1] Is it going to have to physically relocate everything after 2 in memory? Would using a linked list be more efficient if a lot of elements are going to be removed and inserted? ---
**Author:** ![woodzer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/f08c70/32.png) [@woodzer](https://www.ruby-forum.com/u/woodzer)\ **Post date:** [March 14, 2009, 3:41pm UTC](https://www.ruby-forum.com/t/how-do-arrays-in-ruby-work/162851/2 "2009-03-14T15:41:32Z")
slice only returns the value within the range or at index but does not modify the original array. slice![1] would effectively remove value at index 1 from arr. I don’t know how it is implemented. ---
**Author:** ![woodzer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/f08c70/32.png) [@woodzer](https://www.ruby-forum.com/u/woodzer)\ **Post date:** [March 14, 2009, 3:47pm UTC](https://www.ruby-forum.com/t/how-do-arrays-in-ruby-work/162851/3 "2009-03-14T15:47:24Z")
On Sat, Mar 14, 2009 at 10:12 AM, Peter Wu [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > As in how they are organized behind the scenes. > > For example, if I say > > arr = [1, 2, 3, 4] > arr.slice[1] I think you meant either arr.slice(1) or arr[1] arr.slice[1] won’t work since slice requires arguments, and this is being interpreted as (arr.slice)[1] > Is it going to have to physically relocate everything after 2 in memory? > Would using a linked list be more efficient if a lot of elements are > going to be removed and inserted? So far we haven’t done anything which would add or remove anything arr.slice(1) simply returns a reference to the object in the second element of arr. arr is untouched arr.slice(1,3) would return an array containing the second, third and fourth elements, the original array would be untouched. AND The MRI ruby implementation of arrays uses a copy on write scheme, so that both arr and the returned object would actually share memory for the array of references. If one or the other changed then a copy would be triggered. Ruby arrays are implemented rather efficiently both in terms of space and speed. It’s usually best to use them simply and only worry about performance issues when they arise, and when they do, it will probably be something other than “I should have used a linked list instead of an array” – Rick DeNatale Blog: [http://talklikeaduck.denhaven2.com/](http://talklikeaduck.denhaven2.com/) Twitter: [http://twitter.com/RickDeNatale](http://twitter.com/RickDeNatale) WWR: [http://www.workingwithrails.com/person/9021-rick-denatale](http://www.workingwithrails.com/person/9021-rick-denatale) LinkedIn: [http://www.linkedin.com/in/rickdenatale](http://www.linkedin.com/in/rickdenatale) ---
**Author:** ![woodzer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/f08c70/32.png) [@woodzer](https://www.ruby-forum.com/u/woodzer)\ **Post date:** [March 14, 2009, 5:57pm UTC](https://www.ruby-forum.com/t/how-do-arrays-in-ruby-work/162851/4 "2009-03-14T17:57:17Z")
Rick Denatale wrote: > So far we haven’t done anything which would add or remove anything > > arr.slice(1) simply returns a reference to the object in the second > element > of arr. arr is untouched > > arr.slice(1,3) would return an array containing the second, third and > fourth > elements, the original array would be untouched. That’s my mistake, arr.slice!(1) was the intention. But I see what you’re saying. ---
**Author:** ![woodzer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/f08c70/32.png) [@woodzer](https://www.ruby-forum.com/u/woodzer)\ **Post date:** [March 15, 2009, 1:35pm UTC](https://www.ruby-forum.com/t/how-do-arrays-in-ruby-work/162851/5 "2009-03-15T13:35:43Z")
On Mar 14, 2:12 pm, Peter Wu [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > – > Posted viahttp://www.ruby-forum.com/. if you have the array a = [1,2,3,4,5] b = a.slice!(0,3) will end up with a == [4,5] and b == [1,2,3] b = a.slice(0,3) will end up with a == [1,2,3,4,5] and b == [1,2,3] for the last one you can also use b = a[0…2] , you will get the same result