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Removing elements from array Ruby

Posted by: admin November 30, 2017 Leave a comment

Questions:

Let’s say I am trying to remove elements from array a = [1,1,1,2,2,3]. If I perform the following:

b = a - [1,3]

Then I will get:

b = [2,2]

However, I want the result to be

b = [1,1,2,2]

i.e. I only remove one instance of each element in the subtracted vector not all cases. Is there a simple way in Ruby to do this?

Answers:

You may do:

a= [1,1,1,2,2,3]
delete_list = [1,3]
delete_list.each do |del|
    a.delete_at(a.index(del))
end

result : [1, 1, 2, 2]

Questions:
Answers:
[1,3].inject([1,1,1,2,2,3]) do |memo,element|
  memo.tap do |memo|
    i = memo.find_index(e)
    memo.delete_at(i) if i
  end
end

Questions:
Answers:

Not very simple but:

a = [1,1,1,2,2,3]
b = a.group_by {|n| n}.each {|k,v| v.pop [1,3].count(k)}.values.flatten
=> [1, 1, 2, 2]

Also handles the case for multiples in the ‘subtrahend’:

a = [1,1,1,2,2,3]
b = a.group_by {|n| n}.each {|k,v| v.pop [1,1,3].count(k)}.values.flatten
=> [1, 2, 2]

EDIT: this is more an enhancement combining Norm212 and my answer to make a “functional” solution.

b = [1,1,3].each.with_object( a ) { |del| a.delete_at( a.index( del ) ) }

Put it in a lambda if needed:

subtract = lambda do |minuend, subtrahend|
  subtrahend.each.with_object( minuend ) { |del| minuend.delete_at( minuend.index( del ) ) }
end

then:

subtract.call a, [1,1,3]