Ruby: How to Concatenate Array of Arrays into One

Ruby: How to concatenate array of arrays into one

You're looking for #flatten:

concatenated = array_of_arrays.flatten

By default, this will flatten the lists recursively. #flatten accepts an optional argument to limit the recursion depth – the documentation lists examples to illustrate the difference.

Merge arrays in Ruby/Rails

Like this?

⚡️ irb
2.2.2 :001 > [1,2,3] + [4,5,6]
 => [1, 2, 3, 4, 5, 6] 

But you don't have 2 arrays.

You could do something like:

@movie = Movie.first()
@options = Movie.order("RANDOM()").first(3).to_a << @movie

How to efficiently concatenate multiple arrays in Ruby?

If you've already determined that multiple concatenation is the fastest method, you can write it nicer using reduce:

[foo, bar, baz].reduce([], :concat)

Ruby group array of arrays to merge them into one single array based on unique key in arrays

I'm not certain that I understand the question but I expect you may be looking for the following.

arr = [
  ["ABC", "5A2", nil, "88474"],
  ["ABC", nil, "2", "88474"],
  ["ABC", nil, nil, "88474"],
  ["ABC", nil, nil, "88474"],
  ["Jack", "5A2", nil, "05195"],
  ["Jack", nil, "2", "05195"],
  ["Jack", nil, nil, "05195"],
  ["Jack", nil, nil, "05195"]
]

arr.each_with_object({}) do |a, h|
  h.update(a.first=>a) { |_k, oa, na| oa.zip(na).map { |ov, nv| ov.nil? ? nv : ov } }
end.values 
  #=> [["ABC", "5A2", "2", "88474"], ["Jack", "5A2", "2", "05195"]] 

This uses the form of Hash#update (a.k.a. merge!) that employs the block

{ |_k, oa, na| oa.zip(na).map { |ov, nv| ov.nil? ? nv : ov } }

to determine the values of keys that are present in both the hash being built (h) and the hash being merged ({ a.first=>a }). See the doc for a description of the three block variables, _k, oa and na.¹

I can best explain how the calculations procede by salting the code with puts statements and running it with an abbreviated array arr.

arr = [
  ["ABC", "5A2", nil, "88474"],
  ["ABC", nil, "2", "88474"],
  ["Jack", "5A2", nil, "05195"],
  ["Jack", nil, "2", "05195"],
]

arr.each_with_object({}) do |a, h|
  puts "\na = #{a}"
  puts "h = #{h}"
  puts "a.first=>a = #{a.first}=>#{a}"
  h.update(a.first=>a) do |_k, oa, na|
    puts "_k = #{_k}"
    puts "oa = #{oa}"
    puts "na = #{na}"
    a = oa.zip(na)
    puts "oa.zip(na) = #{a}"
    a.map do |ov, nv|
      puts "  ov = #{ov}, nv = #{nv}"
      puts "  ov.nil? ? nv : ov = #{ov.nil? ? nv : ov}"
      ov.nil? ? nv : ov
    end
  end
end.tap { |h| puts "h = #{h}" }.values 
  #=> [["ABC", "5A2", "2", "88474"], ["Jack", "5A2", "2", "05195"]]

The following is displayed.

a = ["ABC", "5A2", nil, "88474"]
h = {}
a.first=>a = ABC=>["ABC", "5A2", nil, "88474"]
(The block is not called here because h does not have a key "ABC")

a = ["ABC", nil, "2", "88474"]
h = {"ABC"=>["ABC", "5A2", nil, "88474"]}
a.first=>a = ABC=>["ABC", nil, "2", "88474"]
_k = ABC
oa = ["ABC", "5A2", nil, "88474"]
na = ["ABC", nil, "2", "88474"]
oa.zip(na) = [["ABC", "ABC"], ["5A2", nil], [nil, "2"], ["88474", "88474"]]
  ov = ABC, nv = ABC
  ov.nil? ? nv : ov = ABC
  ov = 5A2, nv = 
  ov.nil? ? nv : ov = 5A2
  ov = , nv = 2
  ov.nil? ? nv : ov = 2
  ov = 88474, nv = 88474
  ov.nil? ? nv : ov = 88474

a = ["Jack", "5A2", nil, "05195"]
h = {"ABC"=>["ABC", "5A2", "2", "88474"]}
a.first=>a = Jack=>["Jack", "5A2", nil, "05195"]
(The block is not called here because h does not have a key "Jack")

a = ["Jack", nil, "2", "05195"]
h = {"ABC"=>["ABC", "5A2", "2", "88474"], "Jack"=>["Jack", "5A2", nil, "05195"]}
a.first=>a = Jack=>["Jack", nil, "2", "05195"]
_k = Jack
oa = ["Jack", "5A2", nil, "05195"]
na = ["Jack", nil, "2", "05195"]
oa.zip(na) = [["Jack", "Jack"], ["5A2", nil], [nil, "2"], ["05195", "05195"]]
  ov = Jack, nv = Jack
  ov.nil? ? nv : ov = Jack
  ov = 5A2, nv = 
  ov.nil? ? nv : ov = 5A2
  ov = , nv = 2
  ov.nil? ? nv : ov = 2
  ov = 05195, nv = 05195
  ov.nil? ? nv : ov = 05195

h = {"ABC"=>["ABC", "5A2", "2", "88474"], "Jack"=>["Jack", "5A2", "2", "05195"]}

^{1. As is common practice, I began the name of the common key, _k, with an underscore to signal to the reader that it is not used in the block calculation. Often you will see such a block variable represented by an underscore alone.}

How to merge an array of arrays together into a single array?

[["convertible", "2010", "red"], ["convertible", "2010", "green"]].flatten!

Array of arrays merge in Rails

You could use Hash#merge! method with a block for that:

initial = [['Area1', 12345], ['Area2', 54321]].to_h
initial.merge!({'Area1' => 1212 }) { |_,v1,v2| [v1,v2].flatten }
#=> {"Area1"=>[12345, 1212], "Area2"=>54321}

and if you want the result to be an array, you can use

initial.merge!({'Area1' => 1212 }) { |_,v1,v2| [v1,v2].flatten }.to_a

Combine array of array into all possible combinations, forward only, in Ruby

Know your Array#product:

a = [['1','2'],['a','b'],['x','y']]
a.first.product(*a[1..-1]).map(&:join)

---

Related Topics