Excluding first element by value from array

Question

I want to get something like this:

a                       =  [0,1,0,0,1,0,1,0]
a.except(1)           # => [0,0,0,1,0,1,0]
a                     # => [0,1,0,0,1,0,1,0]
a.except(1).except(1) # => [0,0,0,0,1,0]

As you see, the first element of a that equals the argument of except is removed from a.

I can do:

tmp_a = a.dup
tmp_a.delete_at(a.index(1))
tmp_a

but in my opinion, it looks like smell. Is there more elegant one-line solution? (In other words - how to define method "except" for Array?)

UPD

I solved this problem so

class Array
  def except(elem)
    dup.tap{|a| a.delete_at(a.index(elem))}
  end
end

what do you think?

Write a method that encapsulates the element find and slicing. No reason to dupe the array, just take the elements on either side of the value. — Dave Newton
– Dave Newton, Commented Jul 6, 2015 at 12:23
Meta-comment: down-boring an answer because of a misunderstanding seems extreme to me-just comment to clarify and users will police their own content. — Dave Newton
– Dave Newton, Commented Jul 6, 2015 at 12:26
I didn't downvote, however, one of the possible reasons for downvoting mentioned in the tooltip for the downvote button is "This question is unclear", so, if a user feels that the question is unclear, downvoting is perfectly fine. And even if that one user happens to be mistaken, well, there are 4.1 million others which can upvote. — Jörg W Mittag
– Jörg W Mittag, Commented Jul 6, 2015 at 12:38
Gena, I liked your use of tap, so modified my code for Array#difference (at link given in my answer) to use tap in place of cpy = dup, then cpy as the last line. I like the sound of the method, so much so that sometimes I write obj.tap{}.tap{}.tap { |x| ... }. — Cary Swoveland
– Cary Swoveland, Commented Jul 7, 2015 at 7:17

mhutter · Accepted Answer · 2015-07-06 13:40:39Z

2

What's so "hacky" about your solution?

This is also what first came to my mind (started hacking away before reading the entire question :P)

class Array
  def except(elem)
    tmp = self.dup
    tmp.delete_at(self.index(elem))
    tmp
  end
end

Or you can use the power of delete_if (including count I stole from @mudasobwa 's answer:

class Array
  def except(elem, count = 1)
    tmp = self.dup
    memo = 0
    tmp.delete_if { |e| elem == e && (memo += 1) <= count }
  end
end

Or you can slice your array to bits:

class Array
  def except(elem)
    index = self.index(elem)
    self.slice(0, index) + self.slice(index + 1, self.length)
  end
end

answered Jul 6, 2015 at 13:40

mhutter

2,92523 silver badges33 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

Aleksei Matiushkin Over a year ago

Upvoted for slice (which I would rewrite as self[0...index] + self[index+1..-1]).

Stefan Over a year ago

you can replace your slice calls with: reject.with_index { |_, i| i == index }

mhutter Over a year ago

This would be the same as the delete_if solution.

Gena Shumilkin Over a year ago

@Manuel Thanks, it seems good. Look my own solution under UPD in question

mhutter Over a year ago

Ah, very interesting! Didn't know about tap! However, I actually prefer your first version because it's much more readable. Technically it's the same solution.

Aleksei Matiushkin · Accepted Answer · 2015-07-06 13:31:48Z

1

class Array
  def except what, count = 1
    memo = 0
    map do |e| 
      what == e && (memo += 1) <= count ? nil : e
    end.compact
  end
end

The above will remove count occurences of what:

a.except(1, 2) 
#⇒ [0,0,0,0,1,0]

edited Jul 6, 2015 at 13:31

answered Jul 6, 2015 at 13:20

Aleksei Matiushkin

121k12 gold badges109 silver badges174 bronze badges

1 Comment

mhutter Over a year ago

Cool solution, but look out if your array looks like this: [0, nil, 0, 0, nil, 0, nil, 0]. But then, who has nils in his arrays anyways...

Community · Accepted Answer · 2017-05-23 11:58:19Z

1

You could write:

a.difference [1]
  #=> [0,0,0,1,0,1,0] 

a #=> [0,1,0,0,1,0,1,0]

where Array#difference is defined in my answer here.

edited May 23, 2017 at 11:58

CommunityBot

11 silver badge

answered Jul 7, 2015 at 0:51

Cary Swoveland

111k6 gold badges69 silver badges105 bronze badges

2 Comments

Gena Shumilkin Over a year ago

It is the same as that of my solution under UPD in question, cool, thanks

Cary Swoveland Over a year ago

When the argument of difference is an array containing a single element, yes.

Collectives™ on Stack Overflow

Excluding first element by value from array

3 Answers 3

5 Comments

1 Comment

2 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

5 Comments

1 Comment

2 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related