How to loop nested arrays in Ruby

Question

VERY new to Ruby and coding in general. I'm trying to loop through two dimensional arrays but can't figure it out. Here's what I have:

--Use a loop to print out each person on separate lines with their alter egos.

--Bruce Wayne, a.k.a. Batman

people = [
  ["Bruce", "Wayne", "Batman"],
  ["Selina", "Kyle", "Catwoman"],
  ["Barbara", "Gordon", "Oracle"],
  ["Terry", "McGinnis", "Batman Beyond"]
]

index = people[0][0]

first_name = people[0][0]
last_name = people[0][1]
hero_name = people[0][2]

4.times do
  puts first_name + " " + last_name + "," " " + "a.k.a" " " + hero_name
  index = index + 1
end

It does print the first line but then raises an error:

Bruce Wayne, a.k.a Batman
# `+': no implicit conversion of Integer into String (TypeError)

"," " " – I consider that advanced Ruby ;-)

Stefan
– Stefan

2018-05-31 15:11:32 +00:00
Commented May 31, 2018 at 15:11 — Stefan
– Stefan, Commented May 31, 2018 at 15:11

Aleksei Matiushkin · Accepted Answer · 2018-05-31 15:11:06Z

7

In ruby we don’t use loops by index, like for and family; instead we iterate on collections:

people =
  [["Bruce", "Wayne", "Batman"],
   ["Selina", "Kyle", "Catwoman"],
   ["Barbara", "Gordon", "Oracle"],
   ["Terry", "McGinnis", "Batman Beyond"]]

people.each do |first, last, nick|
  puts "#{first} #{last}, a.k.a #{nick}"
end

or

people.each do |first_last_nick|
  *first_last, nick = first_last_nick
  puts [first_last.join(' '), nick].join(', a.k.a ')
end

edited May 31, 2018 at 15:11

answered May 31, 2018 at 14:16

Aleksei Matiushkin

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2 Comments

Stefan Over a year ago

Do we concatenate strings via + in Ruby? ;-)

Aleksei Matiushkin Over a year ago

@Stefan copy-paste is a pure evil :) I always do join as in the second example, to handle nils with compact instead of silly ifs. Fixed btw.

peter · Accepted Answer · 2018-05-31 14:30:46Z

2

Your code produces error because you assign a String to index

index = people[0][0]

and then you use it to count with

index = index + 1

You could have used

index = 0

and

index += 1

A more Rubyesque way would be to enumerate the array and print it like this

people.each do |person|
  puts "#{person.first} #{person[1]}, a.k.a #{person.last}"
end

Which gives

Bruce Wayne, a.k.a Batman
Selina Kyle, a.k.a Catwoman
Barbara Gordon, a.k.a Oracle
Terry McGinnis, a.k.a Batman Beyond

Storing the parts in a variable improves readability but lenghtens the code which in turn diminishes readability, the choice is yours..

As an alternative you could name the indices or decompose like mudasobwa suggests.

Firstname, Lastname, Nickname = 0, 1, 2
people.each do |person|
  puts "#{person[Firstname]} #{person[Lastname]}, a.k.a #{person[Nickname]}"
end

edited May 31, 2018 at 14:30

answered May 31, 2018 at 14:14

peter

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5 Comments

Aleksei Matiushkin Over a year ago

Ever more Rubyesque would be to decompose person instead of using indices :)

Aleksei Matiushkin Over a year ago

@mudasobwa suggested people.each do |fn, ln, hn| instead of indices.

peter Over a year ago

@mudasobwa yep, is better, I like yours more, BTW I used indices OR decompose, so I also changed 'The most' in 'A more' :)

Stefan Over a year ago

Good explanation. Another problem is that index is never used in the OP's code to access the array so it would have produced the same output 4 times.

engineersmnky Over a year ago

@mudasobwa even more Rubyesque would be to build a Person object that knew how to present itself and a People class to contain them :) (and a Soylent Green factory to decompose them)

iGian · Accepted Answer · 2018-05-31 14:40:01Z

0

For your code to work:

4.times do |character|
  puts people[character][0] + " " + people[character][1] + "," " " + "a.k.a" " " + people[character][2]
end

But iterating in ruby is done as answered by others. This is a version using a block {} instead:

people = [["Bruce", "Wayne", "Batman"], ["Selina", "Kyle", "Catwoman"], ["Barbara", "Gordon", "Oracle"], ["Terry", "McGinnis", "Batman Beyond"]]

people.each { |character| puts "#{character [0]}, a.k.a   #{character [1]} #{character [2]}" }

#=> Bruce, a.k.a   Wayne Batman
#=> Selina, a.k.a   Kyle Catwoman
#=> Barbara, a.k.a   Gordon Oracle
#=> Terry, a.k.a   McGinnis Batman Beyond

In general to loop through nested arrays:

people.each do |character|
  character.each do |name|
    puts name
  end
end

edited May 31, 2018 at 14:40

answered May 31, 2018 at 14:22

iGian

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