# Duplicate elements in array **URL:** \ **Category:** ruby-talk\ **Created:** [28 October 2007 12:47 UTC](https://rubytalk.org/t/duplicate-elements-in-array/41728 "2007-10-28T12:47:39Z")\ **Posts on this page:** 15\ **Page:** 1
**Author:** ![Shuaib\_Zahda](https://avatars.discourse-cdn.com/v4/letter/s/b9e5f3/32.png) [@Shuaib\_Zahda](https://rubytalk.org/u/Shuaib_Zahda)\ **Post date:** [28 October 2007 12:47 UTC](https://rubytalk.org/t/duplicate-elements-in-array/41728/1 "2007-10-28T12:47:39Z")
Hello I am trying to output the duplicate elements in an array. I looked into the api of ruby I found uniq method which outputs the array with no duplication. What i want is to know which elements is duplicated. For example array = ["apple", "banana", "apple", "orange"] =\> ["apple", "banana", "apple", "orange"] array.uniq =\> ["apple", "banana", "orange"] I want the method to tell me that apple is the duplicated element I tried this but it does not work array - array.uniq any idea Regards Shuaib > **···** > > -- > Posted via [http://www.ruby-forum.com/](http://www.ruby-forum.com/). ---
**Author:** ![Sean\_O\_Halpin](https://avatars.discourse-cdn.com/v4/letter/s/ac91a4/32.png) [@Sean\_O\_Halpin](https://rubytalk.org/u/Sean_O_Halpin)\ **Post date:** [28 October 2007 13:12 UTC](https://rubytalk.org/t/duplicate-elements-in-array/41728/2 "2007-10-28T13:12:18Z")
think of it right now): array = ["apple", "banana", "apple", "orange"] counts = array.inject(Hash.new {|h,k| h[k] = 0 }) { |hash, item| hash[item] += 1; hash} p counts #=\> {"apple"=\>2, "banana"=\>1, "orange"=\>1} p counts.select { |k,v| v \> 1 }.map{ |k, v| k}.flatten #=\> ["apple"] Regards, Sean > **···** > > On 10/28/07, Shuaib Zahda \ wrote: > > > Hello > > > > I am trying to output the duplicate elements in an array. I looked into > > the api of ruby I found uniq method which outputs the array with no > > duplication. What i want is to know which elements is duplicated. > > For example > > > > array = ["apple", "banana", "apple", "orange"] > > =\> ["apple", "banana", "apple", "orange"] > > array.uniq > > =\> ["apple", "banana", "orange"] > > > > I want the method to tell me that apple is the duplicated element > > > > I tried this but it does not work > > > > array - array.uniq > > > > any idea > > > > Regards > > Shuaib > > -- > > Posted via [http://www.ruby-forum.com/\](http://www.ruby-forum.com/%5C). > > > > Here's one way (I'm sure there must be a simpler approach - just can't ---
**Author:** ![Mohit\_Sindhwani1](https://avatars.discourse-cdn.com/v4/letter/m/dbc845/32.png) [@Mohit\_Sindhwani1](https://rubytalk.org/u/Mohit_Sindhwani1)\ **Post date:** [28 October 2007 13:15 UTC](https://rubytalk.org/t/duplicate-elements-in-array/41728/3 "2007-10-28T13:15:40Z")
Shuaib Zahda wrote: > Hello > > I am trying to output the duplicate elements in an array. I looked into > the api of ruby I found uniq method which outputs the array with no > duplication. What i want is to know which elements is duplicated. > For example > > array = ["apple", "banana", "apple", "orange"] > =\> ["apple", "banana", "apple", "orange"] > array.uniq > =\> ["apple", "banana", "orange"] > > I want the method to tell me that apple is the duplicated element > > I tried this but it does not work > > array - array.uniq > > any idea > > Regards > Shuaib >    > I don't know a good way to do it, but one way to get the result would be to force it into a hash since that eliminates duplicates. I'm sure there's a better way to do it, but here's what I got. array = ["apple", "banana", "apple", "orange", "fat", "cow", "cow"] h = Hash.new duplicates = array.each {|item|     if h.has\_key?(item) then         duplicates \<\< item     else         h[item] = 0 #it doesn't matter what we store     end } puts duplicates Cheers Mohit. ---
**Author:** ![Harry3](https://avatars.discourse-cdn.com/v4/letter/h/54ee81/32.png) [@Harry3](https://rubytalk.org/u/Harry3)\ **Post date:** [28 October 2007 13:55 UTC](https://rubytalk.org/t/duplicate-elements-in-array/41728/4 "2007-10-28T13:55:07Z")
arr,dup = ["apple", "banana", "apple", "orange"], (arr.length-1).times do   a = arr.shift   dup \<\< a if arr.include?(a) end p dup.uniq Harry > **···** > > On 10/28/07, Shuaib Zahda \ wrote: > > > Hello > > > > I am trying to output the duplicate elements in an array. I looked into > > the api of ruby I found uniq method which outputs the array with no > > duplication. What i want is to know which elements is duplicated. > > For example > > > > array = ["apple", "banana", "apple", "orange"] > > =\> ["apple", "banana", "apple", "orange"] > > array.uniq > > =\> ["apple", "banana", "orange"] > > > > I want the method to tell me that apple is the duplicated element > > > > I tried this but it does not work > > > > array - array.uniq > > > > any idea > > > > Regards > > Shuaib > > -- > > Posted via [http://www.ruby-forum.com/\](http://www.ruby-forum.com/%5C). > > -- > A Look into Japanese Ruby List in English > > > **[Kakueki.com is for sale | HugeDomains](https://www.hugedomains.com/domain_profile.cfm?d=kakueki.com)** > > > > Start using this domain right away. Straightforward domain shopping experience. Quick access to your domain. ---
**Author:** ![Mohit\_Sindhwani1](https://avatars.discourse-cdn.com/v4/letter/m/dbc845/32.png) [@Mohit\_Sindhwani1](https://rubytalk.org/u/Mohit_Sindhwani1)\ **Post date:** [28 October 2007 13:16 UTC](https://rubytalk.org/t/duplicate-elements-in-array/41728/5 "2007-10-28T13:16:28Z")
Sean O'Halpin wrote: > **···** > > > On 10/28/07, Shuaib Zahda \ wrote: > >    > > > > > Hello > > > > > > I am trying to output the duplicate elements in an array. I looked into > > > the api of ruby I found uniq method which outputs the array with no > > > duplication. What i want is to know which elements is duplicated. > > > For example > > > > > > array = ["apple", "banana", "apple", "orange"] > > > =\> ["apple", "banana", "apple", "orange"] > > > array.uniq > > > =\> ["apple", "banana", "orange"] > > > > > > I want the method to tell me that apple is the duplicated element > > > > > > I tried this but it does not work > > > > > > array - array.uniq > > > > > > any idea > > > > > > Regards > > > Shuaib > > > -- > > > Posted via [http://www.ruby-forum.com/\](http://www.ruby-forum.com/%5C). > > > > > > Here's one way (I'm sure there must be a simpler approach - just can't > > >      > > > > think of it right now): > > > > array = ["apple", "banana", "apple", "orange"] > > counts = array.inject(Hash.new {|h,k| h[k] = 0 }) { |hash, item| hash[item] > > += 1; hash} > > p counts #=\> {"apple"=\>2, "banana"=\>1, "orange"=\>1} > > p counts.select { |k,v| v \> 1 }.map{ |k, v| k}.flatten #=\> ["apple"] > > > > Regards, > > Sean > > I so have to get the hang of inject, flatten and map. > > Cheers, > Mohit. > 10/28/2007 | 9:16 PM. ---
**Author:** ![Robert\_K1](https://yyz1.discourse-cdn.com/flex029/user_avatar/rubytalk.org/robert_k1/32/1830_2.png) [@Robert\_K1](https://rubytalk.org/u/Robert_K1)\ **Post date:** [28 October 2007 13:40 UTC](https://rubytalk.org/t/duplicate-elements-in-array/41728/6 "2007-10-28T13:40:03Z")
irb(main):007:0\> array = %w{apple banana apple orange} =\> ["apple", "banana", "apple", "orange"] irb(main):008:0\> array.inject(Hash.new(0)) {|ha,e| ha[e]+=1;ha}.delete\_if {|k,v| v==1}.keys =\> ["apple"] Kind regards   robert > **···** > > On 28.10.2007 14:16, Mohit Sindhwani wrote: > > > Sean O'Halpin wrote: > > > > > On 10/28/07, Shuaib Zahda \ wrote: > > > > > > > Hello > > > > > > > > I am trying to output the duplicate elements in an array. I looked into > > > > the api of ruby I found uniq method which outputs the array with no > > > > duplication. What i want is to know which elements is duplicated. > > > > For example > > > > > > > > array = ["apple", "banana", "apple", "orange"] > > > > =\> ["apple", "banana", "apple", "orange"] > > > > array.uniq > > > > =\> ["apple", "banana", "orange"] > > > > > > > > I want the method to tell me that apple is the duplicated element > > > > > > > > I tried this but it does not work > > > > > > > > array - array.uniq > > > > > > > > any idea > > > > > > > > Regards > > > > Shuaib > > > > -- > > > > Posted via [http://www.ruby-forum.com/\](http://www.ruby-forum.com/%5C). > > > > > > > > Here's one way (I'm sure there must be a simpler approach - just can't > > > >      > > > > > > think of it right now): > > > > > > array = ["apple", "banana", "apple", "orange"] > > > counts = array.inject(Hash.new {|h,k| h[k] = 0 }) { |hash, item| hash[item] > > > += 1; hash} > > > p counts #=\> {"apple"=\>2, "banana"=\>1, "orange"=\>1} > > > p counts.select { |k,v| v \> 1 }.map{ |k, v| k}.flatten #=\> ["apple"] ---
**Author:** ![Sean\_O\_Halpin](https://avatars.discourse-cdn.com/v4/letter/s/ac91a4/32.png) [@Sean\_O\_Halpin](https://rubytalk.org/u/Sean_O_Halpin)\ **Post date:** [28 October 2007 17:44 UTC](https://rubytalk.org/t/duplicate-elements-in-array/41728/7 "2007-10-28T17:44:53Z")
Hi, They are definitely worth looking into - inject in particular is a powerful tool (Robert Klemme can make it do anything!). However, the following benchmark shows that a slight modification of your approach is actually pretty efficient. (The modification is to store the duplicates in a hash rather than an array so you can return the list of duplicates using Hash#keys). Regards, Sean # Mohit Sindhwani (with slight adjustment) def duplicates\_1(array)   seen = { }   duplicates = { }   array.each {|item| seen.key?(item) ? duplicates[item] = true : seen[item] = true}   duplicates.keys end # Robert Klemme def duplicates\_2(array)   array.inject(Hash.new(0)) {|ha,e| ha[e]+=1;ha}.delete\_if {|k,v| v==1}.keys end # from facets def duplicates\_3(array)   array.inject(Hash.new(0)){|h,v| h[v]+=1; h}.reject{|k,v| v==1}.keys end require 'benchmark' def do\_benchmark(title, n, methods, \*args, &block)   puts '-' \* 40   puts title   puts '-' \* 40   Benchmark.bm(methods.map{ |x| x.to\_s.length}.max + 2) do |x|     methods.each do |meth|       x.report(meth.to\_s) { n.times do send(meth, \*args, &block) end }     end   end end # get some data (Ubuntu specific I guess - YMMV) array = File.read('/etc/dictionaries-common/words').split(/\n/) # test w/o dups do\_benchmark('no duplicates', 10, [:duplicates\_1, :duplicates\_2, :duplicates\_3], array) # create some duplicates array = array[0..999] \* 100 do\_benchmark('duplicates', 10, [:duplicates\_1, :duplicates\_2, :duplicates\_3], array) \_\_END\_\_ $ ruby bm-duplicates.rb > **···** > > On 10/28/07, Mohit Sindhwani \ wrote: > > > I so have to get the hang of inject, flatten and map. > > > > Cheers, > > Mohit. > > 10/28/2007 | 9:16 PM. > > ---------------------------------------- > no duplicates > ---------------------------------------- >                     user system total real > duplicates\_1 2.200000 0.010000 2.210000 ( 2.215057) > duplicates\_2 5.820000 0.000000 5.820000 ( 5.812414) > duplicates\_3 6.580000 0.010000 6.590000 ( 6.586708) > ---------------------------------------- > duplicates > ---------------------------------------- >                     user system total real > duplicates\_1 1.560000 0.000000 1.560000 ( 1.562587) > duplicates\_2 2.660000 0.000000 2.660000 ( 2.665301) > duplicates\_3 2.590000 0.000000 2.590000 ( 2.595189) ---
**Author:** ![Shuaib\_Zahda](https://avatars.discourse-cdn.com/v4/letter/s/b9e5f3/32.png) [@Shuaib\_Zahda](https://rubytalk.org/u/Shuaib_Zahda)\ **Post date:** [28 October 2007 13:48 UTC](https://rubytalk.org/t/duplicate-elements-in-array/41728/8 "2007-10-28T13:48:23Z")
Thanks a lot guys. It works. I really appreciate your help Cheers Shuaib > **···** > > -- > Posted via [http://www.ruby-forum.com/](http://www.ruby-forum.com/). ---
**Author:** ![Sean\_O\_Halpin](https://avatars.discourse-cdn.com/v4/letter/s/ac91a4/32.png) [@Sean\_O\_Halpin](https://rubytalk.org/u/Sean_O_Halpin)\ **Post date:** [28 October 2007 14:02 UTC](https://rubytalk.org/t/duplicate-elements-in-array/41728/9 "2007-10-28T14:02:16Z")
Succint ~and~ efficient! Do you have a mail filter checking for any posts containing 'inject'? 🙂 Regards, Sean > **···** > > On 10/28/07, Robert Klemme \ wrote: > > > irb(main):007:0\> array = %w{apple banana apple orange} > > =\> ["apple", "banana", "apple", "orange"] > > irb(main):008:0\> array.inject(Hash.new(0)) {|ha,e| > > ha[e]+=1;ha}.delete\_if {|k,v| v==1}.keys > > =\> ["apple"] > > > > Kind regards > > > >         robert ---
**Author:** ![Mohit\_Sindhwani1](https://avatars.discourse-cdn.com/v4/letter/m/dbc845/32.png) [@Mohit\_Sindhwani1](https://rubytalk.org/u/Mohit_Sindhwani1)\ **Post date:** [28 October 2007 18:15 UTC](https://rubytalk.org/t/duplicate-elements-in-array/41728/10 "2007-10-28T18:15:20Z")
Sean O'Halpin wrote: > **···** > > > On 10/28/07, Mohit Sindhwani \ wrote: > >    > > > > > I so have to get the hang of inject, flatten and map. > > > > > > Cheers, > > > Mohit. > > > 10/28/2007 | 9:16 PM. > > >      > > > Hi, > > > > They are definitely worth looking into - inject in particular is a > > powerful tool (Robert Klemme can make it do anything!). However, the > > following benchmark shows that a slight modification of your approach > > is actually pretty efficient. (The modification is to store the > > duplicates in a hash rather than an array so you can return the list > > of duplicates using Hash#keys). > > > > Regards, > > Sean > > > > # Mohit Sindhwani (with slight adjustment) > > def duplicates\_1(array) > >   seen = { } > >   duplicates = { } > >   array.each {|item| seen.key?(item) ? duplicates[item] = true : > > seen[item] = true} > >   duplicates.keys > > end > > > > # Robert Klemme > > def duplicates\_2(array) > >   array.inject(Hash.new(0)) {|ha,e| ha[e]+=1;ha}.delete\_if {|k,v| v==1}.keys > > end > > > > # from facets > > def duplicates\_3(array) > >   array.inject(Hash.new(0)){|h,v| h[v]+=1; h}.reject{|k,v| v==1}.keys > > end > > > > require 'benchmark' > > > > def do\_benchmark(title, n, methods, \*args, &block) > >   puts '-' \* 40 > >   puts title > >   puts '-' \* 40 > >   Benchmark.bm(methods.map{ |x| x.to\_s.length}.max + 2) do |x| > >     methods.each do |meth| > >       x.report(meth.to\_s) { n.times do send(meth, \*args, &block) end } > >     end > >   end > > end > > > > # get some data (Ubuntu specific I guess - YMMV) > > array = File.read('/etc/dictionaries-common/words').split(/\n/) > > > > # test w/o dups > > do\_benchmark('no duplicates', 10, [:duplicates\_1, :duplicates\_2, > > :duplicates\_3], array) > > > > # create some duplicates > > array = array[0..999] \* 100 > > do\_benchmark('duplicates', 10, [:duplicates\_1, :duplicates\_2, > > :duplicates\_3], array) > > > > \_\_END\_\_ > > $ ruby bm-duplicates.rb > > ---------------------------------------- > > no duplicates > > ---------------------------------------- > >                     user system total real > > duplicates\_1 2.200000 0.010000 2.210000 ( 2.215057) > > duplicates\_2 5.820000 0.000000 5.820000 ( 5.812414) > > duplicates\_3 6.580000 0.010000 6.590000 ( 6.586708) > > ---------------------------------------- > > duplicates > > ---------------------------------------- > >                     user system total real > > duplicates\_1 1.560000 0.000000 1.560000 ( 1.562587) > > duplicates\_2 2.660000 0.000000 2.660000 ( 2.665301) > > duplicates\_3 2.590000 0.000000 2.590000 ( 2.595189) > > Thanks Sean! Makes me feel quite nice about it. > > So, hashes are faster than arrays? > > Cheers, > Mohit. > 10/29/2007 | 2:13 AM. ---
**Author:** ![\_Pena\_Botp1](https://avatars.discourse-cdn.com/v4/letter/_/94ad74/32.png) [@\_Pena\_Botp1](https://rubytalk.org/u/_Pena_Botp1)\ **Post date:** [29 October 2007 04:02 UTC](https://rubytalk.org/t/duplicate-elements-in-array/41728/11 "2007-10-29T04:02:28Z")
# $ ruby bm-duplicates.rb # ---------------------------------------- # no duplicates # ---------------------------------------- # user system total real # duplicates\_1 2.200000 0.010000 2.210000 ( 2.215057) # duplicates\_2 5.820000 0.000000 5.820000 ( 5.812414) # duplicates\_3 6.580000 0.010000 6.590000 ( 6.586708) # ---------------------------------------- # duplicates # ---------------------------------------- # user system total real # duplicates\_1 1.560000 0.000000 1.560000 ( 1.562587) # duplicates\_2 2.660000 0.000000 2.660000 ( 2.665301) # duplicates\_3 2.590000 0.000000 2.590000 ( 2.595189) i just tested this using ruby1.9 on a p4 box running windowsxp. i included ruby's group\_by and got surprising results. C:\ruby1.9\bin\>diff test-old.rb test.rb 19a20,24 > #1.9's group\_by > def duplicates\_4(array) >   array.group\_by{|e|e}.select{|\_,k| k.size\>1}.keys > end 26c31 \< Benchmark.bm(methods.map{ |x| x.to\_s.length}.max + 2) do |x| > **···** > > From: Sean O'Halpin [mailto:sean.ohalpin@gmail.com] > --- > > >   Benchmark.bmbm(methods.map{ |x| x.to\_s.length}.max + 2) do |x| > > 34c39 > \< array = File.read('/etc/dictionaries-common/words').split(/\n/) > --- > > > array = File.read('american-english').split(/\n/) > > 38c43 > \< :duplicates\_3], array) > --- > > > :duplicates\_3,:duplicates\_4], array) > > 43c48 > \< :duplicates\_3], array) > --- > > > :duplicates\_3,:duplicates\_4], array) > > C:\ruby1.9\bin\> > > C:\ruby1.9\bin\>ruby test.rb > ---------------------------------------- > no duplicates > ---------------------------------------- > Rehearsal ------------------------------------------------- > duplicates\_1 7.609000 0.094000 7.703000 ( 7.984000) > duplicates\_2 10.438000 0.109000 10.547000 ( 11.608000) > duplicates\_3 14.609000 0.219000 14.828000 ( 14.874000) > duplicates\_4 11.422000 0.141000 11.563000 ( 14.201000) > --------------------------------------- total: 44.641000sec > >                     user system total real > duplicates\_1 7.219000 0.125000 7.344000 ( 8.109000) > duplicates\_2 9.844000 0.078000 9.922000 ( 10.374000) > duplicates\_3 14.391000 0.172000 14.563000 ( 18.498000) > duplicates\_4 11.172000 0.172000 11.344000 ( 12.998000) > ---------------------------------------- > duplicates > ---------------------------------------- > Rehearsal ------------------------------------------------- > duplicates\_1 3.375000 0.000000 3.375000 ( 3.765000) > duplicates\_2 3.218000 0.000000 3.218000 ( 3.828000) > duplicates\_3 3.250000 0.000000 3.250000 ( 3.672000) > duplicates\_4 2.032000 0.047000 2.079000 ( 2.077000) > --------------------------------------- total: 11.922000sec > >                     user system total real > duplicates\_1 3.375000 0.000000 3.375000 ( 3.437000) > duplicates\_2 3.188000 0.000000 3.188000 ( 3.218000) > duplicates\_3 3.219000 0.015000 3.234000 ( 3.281000) > duplicates\_4 1.844000 0.000000 1.844000 ( 1.859000) > > C:\ruby1.9\bin\> > > kind regards -botp ---
**Author:** ![Sean\_O\_Halpin](https://avatars.discourse-cdn.com/v4/letter/s/ac91a4/32.png) [@Sean\_O\_Halpin](https://rubytalk.org/u/Sean_O_Halpin)\ **Post date:** [28 October 2007 18:47 UTC](https://rubytalk.org/t/duplicate-elements-in-array/41728/12 "2007-10-28T18:47:28Z")
It depends what you're doing with them and how big they are. But in this instance, I changed your solution to use a hash because you were appending the duplicates to an array which resulted in adding an entry to that array every time you detected a duplicate. This didn't show up in your example because your data contained at most two instances of an item. If you change your example to: array = ["apple", "banana", "apple", "orange", "fat", "cow", "cow", "apple", "apple"] h = Hash.new duplicates = array.each {|item|    if h.has\_key?(item) then        duplicates \<\< item    else        h[item] = 0 #it doesn't matter what we store    end } puts duplicates it outputs apple cow apple apple which is probably not what you want. Regards, Sean > **···** > > On 10/28/07, Mohit Sindhwani \ wrote: > > > Thanks Sean! Makes me feel quite nice about it. > > > > So, hashes are faster than arrays? > > > > Cheers, > > Mohit. > > 10/29/2007 | 2:13 AM. ---
**Author:** ![Robert\_K1](https://yyz1.discourse-cdn.com/flex029/user_avatar/rubytalk.org/robert_k1/32/1830_2.png) [@Robert\_K1](https://rubytalk.org/u/Robert_K1)\ **Post date:** [29 October 2007 10:28 UTC](https://rubytalk.org/t/duplicate-elements-in-array/41728/13 "2007-10-29T10:28:20Z")
> \> > \> irb(main):007:0\> array = %w{apple banana apple orange} > \> =\> ["apple", "banana", "apple", "orange"] > \> irb(main):008:0\> array.inject(Hash.new(0)) {|ha,e| > \> ha[e]+=1;ha}.delete\_if {|k,v| v==1}.keys > \> =\> ["apple"] > \> > Succint ~and~ efficient! Thanks! > Do you have a mail filter checking for any posts > containing 'inject'? 🙂 I don't need that since most of them were written by me. 🙂 (slight exaggeration) \*chuckle\* Kind regards robert > **···** > > 2007/10/28, Sean O'Halpin \: > > > On 10/28/07, Robert Klemme \ wrote: ---
**Author:** ![Jimmy\_Kofler](https://avatars.discourse-cdn.com/v4/letter/j/e495f1/32.png) [@Jimmy\_Kofler](https://rubytalk.org/u/Jimmy_Kofler)\ **Post date:** [28 October 2007 21:31 UTC](https://rubytalk.org/t/duplicate-elements-in-array/41728/14 "2007-10-28T21:31:53Z")
> Duplicate elements in array > Posted by Shuaib Zahda (shuaib85) on 28.10.2007 13:47 > Hello > > I am trying to output the duplicate elements in an array. I looked into > the api of ruby I found uniq method which outputs the array with no > duplication. What i want is to know which elements is duplicated. Here's yet another way to do it: [http://snippets.dzone.com/posts/show/4148](http://snippets.dzone.com/posts/show/4148) Cheers, j.k. > **···** > > -- > Posted via [http://www.ruby-forum.com/\](http://www.ruby-forum.com/%5C). ---
**Author:** ![Mohit\_Sindhwani1](https://avatars.discourse-cdn.com/v4/letter/m/dbc845/32.png) [@Mohit\_Sindhwani1](https://rubytalk.org/u/Mohit_Sindhwani1)\ **Post date:** [29 October 2007 03:44 UTC](https://rubytalk.org/t/duplicate-elements-in-array/41728/15 "2007-10-29T03:44:24Z")
Sean O'Halpin wrote: > **···** > > > On 10/28/07, Mohit Sindhwani \ wrote: > >    > > > > > Thanks Sean! Makes me feel quite nice about it. > > > > > > So, hashes are faster than arrays? > > > > > > Cheers, > > > Mohit. > > > 10/29/2007 | 2:13 AM. > > >      > > > It depends what you're doing with them and how big they are. But in > > > this instance, I changed your solution to use a hash because you were > > > appending the duplicates to an array which resulted in adding an entry > > > to that array every time you detected a duplicate. This didn't show up > > > in your example because your data contained at most two instances of > > > an item. If you change your example to: > > > > array = ["apple", "banana", "apple", "orange", "fat", "cow", "cow", > > "apple", "apple"] > > h = Hash.new > > duplicates = > > > > array.each {|item| > >    if h.has\_key?(item) then > >        duplicates \<\< item > >    else > >        h[item] = 0 #it doesn't matter what we store > >    end > > } > > > > puts duplicates > > > > it outputs > > > > apple > > cow > > apple > > > > which is probably not what you want. > > > > Regards, > > Sean > > Thanks for the explanation, Sean. Actually, I guess it's not clear if the OP wants to know each occurrence of the duplicates or just the list of duplicates. But, there are now solutions for both cases! > > Cheers, > Mohit. > 10/29/2007 | 11:44 AM.