How to check if array shares elements with another array in Ruby?

Question

I'm currently trying to see if an array of records shares elements with another array.

I'm using the splat operator for a conditional like this:

if @user.tags.include?(*current_tags)
    # code
end

This works when tags are present, but returns this error when current_tags are empty.

wrong number of arguments (given 0, expected 1)

This happens a lot in my app so I was wondering if there are any alternatives to achieving this same functionality but in other way that won't blow up if current_tags is an empty array.

this will only work if current_tags has exactly 1 element. I would recommend not using include? here — max pleaner
– max pleaner, Commented Oct 24, 2018 at 5:29
What's the expected behavior if current_tags is empty – should the conditional evaluate or skip the code block in that case? — Stefan
– Stefan, Commented Oct 24, 2018 at 6:24

d11wtq · Accepted Answer · 2018-10-24 05:28:35Z

17

You can use an intersection to solve this problem instead. The intersection of two arrays is an array containing only the elements present in both. If the intersection is empty, the arrays had nothing in common, else the arrays had the elements from the result in common:

if (current_tags & @user.tags).any?
  # ok
end

answered Oct 24, 2018 at 5:28

d11wtq

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1 Comment

Alvaro Alday Over a year ago

All the answers were good, but this is the simplest, easiest to understand. Thanks.

Ilya Konyukhov · Accepted Answer · 2018-10-24 05:26:40Z

4

Another trick to do the same is:

if current_tags.any? { |tag| @user.tags.include?(tag) }
  ...
end

if you want to be sure that at least one of the current_tags is in the array of @user.tags, or

if current_tags.all? { |tag| @user.tags.include?(tag) }
  ...
end

in case all tags should be there.

Works fine with empty current_tags as well.

answered Oct 24, 2018 at 5:26

Ilya Konyukhov

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Comments

Anand · Accepted Answer · 2018-10-24 04:55:45Z

0

Add one more condition if current_tags.present?

if current_tags.present? && @user.tags.include?(*current_tags)
    # code
end

As

2.3.1 :002 > [].present?
 => false

answered Oct 24, 2018 at 4:55

Anand

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1 Comment

max pleaner Over a year ago

This doesn't work if current_tags has more than 1 element - include? takes 1 and only 1 arg

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