how to create an array that excludes items from another array in Ruby

Question

I have two arrays with different attributes for the objects contained in each.

participants

guests

The only field in common is provider_user_id

I want to do something like this

all_people = participants.map {|p| p.provider_user_id <> guests.provider_user_id }

This is probably not correct.

How can eliminate those participants who are also in the guests array?

Does all_people equate to guests who are not participants? Or are you wanting the combination of guests and participants but you want to avoid including the same person twice? — Andrew Grimm
– Andrew Grimm, Commented Sep 27, 2011 at 3:35

Andrew Grimm · Accepted Answer · 2011-09-27 03:33:14Z

1

The following works, but I'd be interested if there's anything more concise.

guest_provider_ids = guest.map(&:provider_id)
non_guest_participants = participants.reject do |participant|
  guest_provider_ids.include?(participant.provider_user_id)
end

answered Sep 27, 2011 at 3:33

Andrew Grimm

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Chuck Bergeron · Accepted Answer · 2011-09-27 03:36:59Z

1

Could work...

guests.each { |g| participants << g }
guests.uniq! { |g| g.provider_user_id }

This (should) combine the two arrays first, then removes any duplicates based on the key.

answered Sep 27, 2011 at 3:36

Chuck Bergeron

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2 Comments

Chuck Bergeron Over a year ago

That said, I didn't test it out of pure tiredness. It's probably not a good time for me to being handing out advice on StackOverflow. ;)

Andrew Grimm Over a year ago

Ah - it was added in 1.9.2. Warning: if you try using it on an older version, it'll just silently ignore the block.

Andrew Grimm · Accepted Answer · 2011-10-04 02:12:58Z

1

Good answers but don't forget about |. For 1.9

p (guests | participants).uniq!{|g| g.provider_user_id}

For 1.8

p (guests | participants).reject{|p| guests.map{|g| g.provider_user_id}.include?(p.provider_user_id)}

edited Oct 4, 2011 at 2:12

Andrew Grimm

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answered Sep 28, 2011 at 5:22

pguardiario

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1 Comment

Andrew Grimm Over a year ago

Don't forget about the | character? I guess we'd better not forget the { and the } either, right?

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