Mapping Values from Two Array in Ruby

Mapping values from two array in Ruby

@Michiel de Mare

Your Ruby 1.9 example can be shortened a bit further:

weights.zip(data).map(:*).reduce(:+)

Also note that in Ruby 1.8, if you require ActiveSupport (from Rails) you can use:

weights.zip(data).map(&:*).reduce(&:+)

How to loop over two arrays and create a map in Ruby

If what you need is an array of hashes, where every hash has the keys shape and color, then you can use product between array1 and array2 and then just map the result of that:

array1.product(array2).map { |shape, color| { shape: shape, color: color } }
# [{:shape=>"square", :color=>"red"}, {:shape=>"square", :color=>"blue"}, {:shape=>"circle", :color=>"red"}, {:shape=>"circle", :color=>"blue"}, {:shape=>"triagle", :color=>"red"}, {:shape=>"triagle", :color=>"blue"}]

ruby map a function over multiple arrays

Use zip to combine each element with its corresponding in two element array and than map

asc.zip(dsc).map { |a, b| a * b }
 => [0, 4, 6, 6, 4, 0] 

How can I map values in two different arrays as properties on an equivalent array of objects?

a.zip(b).map { |args| Obj.new(*args) }

Per your edit:

a.zip(b).map { |(a, b)| Obj.new(a, b) }

Ruby join two arrays by key value

This is a way to do it.

sounds = arr2[0]
results = arr1.map do |animal|
  "#{animal["n"]}: #{sounds[animal["id"]]}"
end
puts results
# => cat: meow
# => dog: woof

Seems like the second array should just be a hash instead. There's no point creating an array if there's only one element in it and that number won't change.

pointless one-liner (don't use this)

puts arr1.map { |x| "#{x["n"]}: #{arr2[0][x["id"]]}" }

Combine two arrays in Ruby?

I would transform the two arrays to lookup hashes. Then collect all the ids to iterate. Map the ids into the foo and bar values, then zip them together.

foo_lookup = foo.to_h { |id| [id, {id: id}] } # change `{id: id}` into `id` for the other output
bar_lookup = bar.to_h { |item| [item[:id], item] }

ids = foo_lookup.keys | bar_lookup.keys

res = ids.map(&foo_lookup).zip(ids.map(&bar_lookup))
#=> [[{:id=>1}, nil], [{:id=>2}, {:id=>2}], [nil, {:id=>4}]]

Returning Multiple Values From Map

Use Enumerable#flat_map

b = [0, 3, 6]
a = b.flat_map { |x| [x, x+1, x+2] }
a # => [0, 1, 2, 3, 4, 5, 6, 7, 8]

What is the best way to merge two arrays (element + element), if elements itself are arrays

[Array1, Array2].transpose.map(&:flatten) 
=> [[1, 2, 1, 4], [8, 11], [2, 3, 3, 6]]

RubyGuides: "Turn Rows Into Columns With The Ruby Transpose Method"

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Each step explained:

[Array1, Array2]
=> [[[1, 2], [], [2, 3]], 
    [[1, 4], [8, 11], [3, 6]]]

Create a grid like array.

[Array1, Array2].transpose
=> [[[1, 2], [1, 4]], [[], [8, 11]], [[2, 3], [3, 6]]]

transpose switches rows and columns (close to what we want)

[Array1, Array2].transpose.map(&:flatten)
=> [[1, 2, 1, 4], [8, 11], [2, 3, 3, 6]]

flatten gets rid of the unnecessary nested arrays (here combined with map to access nested arrays)

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