Combine two Arrays into Hash

Question

I've got two Arrays:

members     = ["Matt Anderson", "Justin Biltonen", "Jordan Luff", "Jeremy London"]
instruments = ["guitar, vocals", "guitar", "bass", "drums"]

What I would like to do is combine these so that the resulting data structure is a Hash like so:

{"Matt Anderson"=>["guitar", "vocals"], "Justin Biltonen"=>"guitar", "Jordan Luff"=>"bass", "Jeremy London"=>"drums"}

Note the value for "Matt Anderson" is now an Array instead of a string. Any Ruby wizards care to give this a shot?

I know Hash[*members.zip(instruments).flatten] combines them almost the way I want, but what about turning the "guitars, vocals" string into an array first?

Answer 1

As Rafe Kettler posted, using zip is the way to go.

Hash[members.zip(instruments)] 

Answer 2

Use map and split to convert the instrument strings into arrays:

instruments.map {|i| i.include?(',') ? (i.split /, /) : i}

Then use Hash[] and zip to combine members with instruments:

Hash[members.zip(instruments.map {|i| i.include?(',') ? (i.split /, /) : i})]

to get

{"Jeremy London"=>"drums",
 "Matt Anderson"=>["guitar", "vocals"],
 "Jordan Luff"=>"bass",
 "Justin Biltonen"=>"guitar"}

If you don't care if the single-item lists are also arrays, you can use this simpler solution:

Hash[members.zip(instruments.map {|i| i.split /, /})]

which gives you this:

{"Jeremy London"=>["drums"],
 "Matt Anderson"=>["guitar", "vocals"],
 "Jordan Luff"=>["bass"],
 "Justin Biltonen"=>["guitar"]}

Answer 3

Example 01

k = ['a', 'b', 'c']
v = ['aa', 'bb']
h = {}

k.zip(v) { |a,b| h[a.to_sym] = b } 
# => nil

p h 
# => {:a=>"aa", :b=>"bb", :c=>nil}

Example 02

k = ['a', 'b', 'c']
v = ['aa', 'bb', ['aaa','bbb']]
h = {}

k.zip(v) { |a,b| h[a.to_sym] = b }
p h 
# => {:a=>"aa", :b=>"bb", :c=>["aaa", "bbb"]}

Answer 4

This is the best and cleanest way to do what you want.

Hash[members.zip(instruments.map{|i| i.include?(',') ? i.split(',') : i})]

Enjoy!

Answer 5

h = {}
members.each_with_index do |el,ix|
    h[el] = instruments[ix].include?(",") ? instruments[ix].split(",").to_a : instruments[ix]
end
h

Answer 6

members.inject({}) { |m, e| t = instruments.delete_at(0).split(','); m[e] = t.size > 1 ? t : t[0]; m }

If you don't care about 1-element arrays in the result, you can use:

members.inject({}) { |m, e| m[e] = instruments.delete_at(0).split(','); m }

Answer 7

h = {}

members.each_with_index {|item, index|
     h.store(item,instruments[index].split)
}

Answer 8

When approaching a programming task like this, it helps to think in terms of step-wise data transformations.

You have two arrays: 1) band members and 2) instruments they play. BUT sometimes a member plays more than one instrument. This means there's another entity implicitly lurking in there.

This entity can be made explicit by introducing a logical condition:

if member plays multiple parts:
  return an array containing those parts
 else:
  return the instrument

Once you've transformed your original instruments array according to this condition, you're ready to merge it into a Hash with members:

members     = ["Matt Anderson", "Justin Biltonen", "Jordan Luff", "Jeremy London"]
instruments = ["guitar, vocals", "guitar", "bass", "drums"]

def band(members, instruments)
 roles = instruments.map do |ins|
  arr = ins.split(", ")
  arr.length > 1 ?  arr : ins
 end
 Hash[members.zip(roles)]
end


require 'minitest/spec'
require 'minitest/autorun'

describe "creates a band out of members and instruments" do
 it "combines arrays into a hash" do

  band(members, instruments).must_equal({
     "Matt Anderson"   => ["guitar", "vocals"],
     "Justin Biltonen" => "guitar",
     "Jordan Luff"     => "bass",
     "Jeremy London"   => "drums"
    })

 end
end