ruby array of arrays get duplicate string array

Question

I have this array of arrays:

arr =[["twitter.com", 9], ["twitter.com", 9], ["google.com", 11], ["paypal.me", 11],
      ["twitter.com", 11], ["yahoo.com", 12], ["google.com", 14], ["twitter.com", 17],
      ["twitter.com", 18], ["youtube.com", 31]]

How can I extract the arrays that have duplicate strings and get:

[["twitter.com", 9], ["twitter.com", 9], ["google.com", 11], ["twitter.com", 11],
 ["google.com", 12], ["twitter.com", 17], ["twitter.com", 18]]

Then add the value of the strings that are duplicate:

[["twitter.com", 64], ["google.com", 25]]

And end up with a new array :

[["twitter.com", 64], ["youtube.com", 31], ["google.com", 25],
 ["yahoo.com", 12],["paypal.me", 11]]

I tried:

array.select{|element| array.count(element) > 1 }

But was getting: [["twitter.com", 9], ["twitter.com", 9]

Have you attempted the problem yourself? What did you try?

Sagar Pandya
– Sagar Pandya

2017-11-06 19:03:13 +00:00
Commented Nov 6, 2017 at 19:03 — Sagar Pandya
– Sagar Pandya, Commented Nov 6, 2017 at 19:03

Ilya · Accepted Answer · 2017-11-06 18:20:56Z

3

Just count all sites with each_with_object:

array.each_with_object(Hash.new(0)) {|(site, count), memo| memo[site] += count}
#=> {"twitter.com"=>64, "google.com"=>25, 
#    "paypal.me"=>11, "yahoo.com"=>12, "youtube.com"=>31}

You can simply convert the result to array by adding to_a, but IMO hash is enough for your issue.

answered Nov 6, 2017 at 18:20

Ilya

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3 Comments

mamesaye Over a year ago

How would you order new array value ascendent?

Ilya Over a year ago

@mamesaye, .sort_by {|_, v| -v}

tokland Over a year ago

@mamesaye: That's not idiomatic, whenever you can, use sort_by instead of sort.

tokland · Accepted Answer · 2017-11-07 18:40:13Z

2

Functional approach:

pairs.
  group_by { |k, v| k }.
  map { |k, ps| [k, ps.map { |k, v| v }.reduce(:+)] }.
  sort_by { |k, v| -v }
#=> [["twitter.com", 64], ["youtube.com", 31], ["google.com", 25],
#    ["yahoo.com", 12], ["paypal.me", 11]]

edited Nov 7, 2017 at 18:40

answered Nov 6, 2017 at 21:47

tokland

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4 Comments

Ilya Over a year ago

What do you mean by functional?

tokland Over a year ago

@Ilya: Functional programming, immutable data. en.wikipedia.org/wiki/Functional_programming slideshare.net/tokland/functional-programming-with-ruby-9975242

Ilya Over a year ago

I know what community means by this term:) IMO, this code is about immutable data only.

tokland Over a year ago

It's all very subjective, ofc, but whenever a code uses immutable structures, modular abstractions, higher-order functions, ..., I think it may qualify as "functional". How would you write it in functional style with Ruby?

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