ruby language - merge an array into another by finding same element

Question

A = [
  { :id => 1, :name => 'good', :link => nil },
  { :id => 2, :name => 'bad', :link => nil } 
]

B = [
  { :id => 3, :name => 'good' },
  { :id => 4, :name => 'good' }, 
  { :id => 5, :name => 'bad' } 
]

I need to merge array B into A so that :link in array A includes the entry in array B if :name is the same value in each array.

For example, after processing array A should be:

A = [
  { :id => 1, :name => 'good', :link => [{ :id => 3, :name => 'good' }, { :id => 4, :name => 'good' }] },
  { :id => 2, :name => 'bad', :link => [{ :id => 5, :name => 'bad' }] }
]

thanks.

hint: don't upload, create new objects (so merge instead of update). — tokland
– tokland, Commented Feb 27, 2012 at 13:33
@tokland: sorry, you are right. bad should have link (id=5). thanks. — hey mike
– hey mike, Commented Feb 27, 2012 at 15:04

Joachim Isaksson · Accepted Answer · 2012-02-27 12:09:24Z

3

The short version;

a.each { | item | item[:link] = b.find_all { | x | x[:name] == item[:name] } }

Demo here.

answered Feb 27, 2012 at 12:09

Joachim Isaksson

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1 Comment

DGM Over a year ago

of course, this only updates existing values in a, it doesn't create new keys from b if they exist in ba but not a.

megas · Accepted Answer · 2012-02-27 11:51:36Z

1

In ruby the constants begin with an uppercase letter, so you should use lowercase letter: A => a, B => b

a.each do |ha|
  b.each do |hb|
    if ha[:name] == hb[:name]
      ha[:link] |= []
      ha[:link] << hb
    end
  end
end

answered Feb 27, 2012 at 11:51

megas

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Comments

tokland · Accepted Answer · 2012-02-27 15:24:21Z

0

Functional approach:

B_grouped = B.group_by { |h| h[:name]  }
A2 = A.map { |h| h.merge(:link => B_grouped[h[:name]]) }
#=> [{:link=>[{:name=>"good", :id=>3}, {:name=>"good", :id=>4}], :name=>"good", :id=>1},
#    {:link=>[{:name=>"bad", :id=>5}], :name=>"bad", :id=>2}]

edited Feb 27, 2012 at 15:24

answered Feb 27, 2012 at 13:32

tokland

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