Trying to display only duplicate values

I'm trying to display only the duplicate value in an array which just holds names.

So for instance, my code is:

  <%= s= arrayOfStuff %> 
  <%= t= arrayOfStuff.uniq %>

which displays

["UK01USV005", "NJ08APP516", "NJ08MHF001", "UK01USV505", "NY01MHF0006", "UK01USV525", "UK01USV005", "NJ08APP515", "NJ08MHF002"]
["UK01USV005", "NJ08APP516", "NJ08MHF001", "UK01USV505", "NY01MHF0006", "开发者_JAVA技巧UK01USV525", "NJ08APP515", "NJ08MHF002"]

so theortically when I do s-t it should give me the duplicate value which in this case is UK01USV005, however the results I get is an empty array which obviously looks like this: [].

Any ideas why that could be?

arrayOfStuff.group_by {|e| e}.select { |k,v| v.size > 1}.keys

should work fine.

You're wrong.

["a", "a", "a"] - ["a"]
#=> []

You can try this in your case:

a.inject([]){|ar, item| b.include?(item) ? b.delete(item) : ar << item; ar}
#=> ["UK01USV005"]

or with your original Array

arrayOfStuff.select{|item| arrayOfStuff.count(item) > 1}.uniq

Subtracting an array from an array removes all the matching objects, not only the first one.

See the simple test:

[1,2,1] - [1] # => [2]

So, if you want to scan for duplicate values, you may try group_by (as lucapette managed to suggest much faster) ;-)

You can do something like:

["UK01USV005", "NJ08APP516", "NJ08MHF001", "UK01USV505", "NY01MHF0006", "UK01USV525", "NJ08APP515", "NJ08MHF002"] && ["UK01USV005", "NJ08APP516", "NJ08MHF001", "UK01USV505", "NY01MHF0006", "UK01USV525", "UK01USV005", "NJ08APP515", "NJ08MHF002"]

=> ["UK01USV005", "NJ08APP516", "NJ08MHF001", "UK01USV505", "NY01MHF0006", "UK01USV525", "UK01USV005", "NJ08APP515", "NJ08MHF002"]

Which is what you are looking for?