Finding element occurring in each array in Rails

Question

I have the following array: items = [[573, 574], [573, 574], [573], [573, 574]]

How to find element which is occurring on each array ? From this array i want to get only "573" Anyone could help me ?

Cary Swoveland · Accepted Answer · 2017-09-24 00:34:21Z

3

def appears_in_all(arr)
  arr.reduce(:&)
end

appears_in_all [[573, 574], [573, 574], [573], [573, 574]]           #=> [573]
appears_in_all [[573, 574], [573, 574], [573, 574, 578], [573, 574]] #=> [573, 574]
appears_in_all [[573, 574], [573, 574], [573], [573, 574], [2, 4]]   #=> []

answered Sep 24, 2017 at 0:34

Cary Swoveland

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Simple Lime · Accepted Answer · 2017-09-23 20:30:37Z

3

You can find the smallest sub array in items (to limit the search set) and then select all the elements from that array that appear in all the other arrays in items:

items.min_by(&:length).select do |element|
  items.all? { |sub_array| sub_array.include?(element) }
end
# => [573]

if it's guaranteed only a single element is in all of them, you can use detect instead of select

answered Sep 23, 2017 at 20:30

Simple Lime

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1 Comment

Sebastián Palma Over a year ago

I must use the comments to say is a very clean solution.

aromero · Accepted Answer · 2017-09-23 20:27:45Z

1

items.flatten.uniq.select{|x| items.map{|y| y.include? x}.all?}

answered Sep 23, 2017 at 20:27

aromero

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