Return unique values of an array without using `uniq`

Question

For a challenge, I'm trying to return the unique values of an array without using uniq. This is what I have so far, which doesn't work:

def unique
   unique_arr = []
   input_arr.each do |word|
     if word != unique_arr.last
       unique_arr.push word
     end
   end
   puts unique_arr
end
input = gets.chomp
input_arr = input.split.sort
input_arr.unique

My reasoning here was that if I sorted the array first before I iterated through it with each, I could push it to unique_arr without repetition being a possibility considering if it's a duplicate, the last value pushed would match it.

Am I tackling this the wrong way?

Yeah I'm only a beginner. I hadn't even heard of uniq until the challenge told me not to use it. — Kevin
– Kevin, Commented Feb 8, 2016 at 14:32
Your question was misleading. If it is meant to work only on a sorted array, then you should have written so, and not just implying that (subtlely) in the code. And you should note that that is different from what uniq does. — sawa
– sawa, Commented Feb 8, 2016 at 14:57
If you are going to apply split on input, what is the point of doing chomp? — sawa
– sawa, Commented Feb 8, 2016 at 14:59

sawa · Accepted Answer · 2016-02-08 14:55:18Z

4

Yes, you are making at least two mistakes.

If you want to call it as input_arr.unique with input_arr being an array, then you have to define the method on Array. You have input_arr within your method body, which comes from nowhere.
puts in the last line of your code outputs to the terminal, but makes the method return nil, which makes it behave differently from uniq.

It can be fixed as:

class Array
  def unique
    unique_arr = []
    each do |word|
      unique_arr.push(word) unless unique_arr.last == word
    end
    unique_arr
  end
end

edited Feb 8, 2016 at 14:55

answered Feb 8, 2016 at 13:50

sawa

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Comments

sawa · Accepted Answer · 2016-02-08 14:05:02Z

4

A unique array? That sounds like a Set to me:

require 'set'

Set.new([1,2,3,2,3,4]).to_a
#=> [1,2,3,4]

edited Feb 8, 2016 at 14:05

sawa

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answered Feb 8, 2016 at 14:04

spickermann

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1 Comment

Andrey Deineko Over a year ago

yea, Set is a perfect solution!

Dave Schweisguth · Accepted Answer · 2016-02-09 13:52:05Z

4

Here's a concise way to do it that doesn't explicitly use functionality from another class but probably otherwise misses the point of the challenge:

class Array
  def unique
    group_by(&:itself).keys
  end
end

edited Feb 9, 2016 at 13:52

answered Feb 8, 2016 at 13:55

Dave Schweisguth

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Comments

Lukas Baliak · Accepted Answer · 2016-02-08 14:22:31Z

0

I try this three options. Just for challenge

class Array
  def unique
    self.each_with_object({}) { |k, h| h[k] = k }.keys
  end

  def unique2
    self.each_with_object([]) { |k, a| a << k unless a.include?(k) }
  end

  def unique3
    arr = []
    self.map { |k| arr << k unless arr.include?(k) }
    arr
  end
end

edited Feb 8, 2016 at 14:22

answered Feb 8, 2016 at 14:17

Lukas Baliak

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3 Comments

sawa Over a year ago

In unique, what is the point of making the hash value (not the key) k? Won't a value like true suffice and be simpler?

sawa Over a year ago

In unique3, why are you explicitly writing self? What is the point of using map?

Lukas Baliak Over a year ago

@sawa In unique I just try to show more ways to do this "challenge", ofc you are right with the true insted of k. In unique3 i use map bcs of more speed and like "new" way have uniq values.

Wand Maker · Accepted Answer · 2016-02-08 18:28:06Z

0

Here is one more way to do this:

uniques = a.each.with_object([]) {|el, arr| arr << el if not arr.include?(el)}

answered Feb 8, 2016 at 18:28

Wand Maker

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Comments

sawa · Accepted Answer · 2016-02-08 14:13:41Z

-1

That's so easy if you see it this way:

a = [1,1,2,3,4]
h = Hash.new
a.each{|q| h[q] = q}
h.values

and this will return:

[1, 2, 3, 4]

edited Feb 8, 2016 at 14:13

sawa

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answered Feb 8, 2016 at 13:48

Abdul Baig

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