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Level Up Your Ruby Skillz: Working With Arrays

Molly Struve (she/her) on May 08, 2019

When I first started out, there was a senior engineer that I worked with who was a wizard when it came to working with arrays. He taught me all the...

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Kobe Raypole • May 8 '19

Awesome article! I use the with_index method quite often. Another option is each_with_index.

At first, there appears to be no difference until you take into account that with_index accepts an optional "start index". Therefore you can start your array index at 1 by doing

result = ['a', 'b', 'c'].map.with_index(1) do |letter, index|
  "#{letter}:#{index}"
end
# result = ["a:1", "b:2", "c:3"]

Molly Struve (she/her) • May 8 '19

WHAT?!!!!!! I had no clue, thank you for sharing!!!

Aidan Walters-Williams • May 9 '19 • Edited

Fantastic article Molly! I have been using

result = [1, 2, 3].map do |number|
  ['a', 'b', 'c'].map do |letter|
    "#{number}:#{letter}"
  end
end
result.flatten

for ages without knowing there was a better alternative!

Luke Inglis • May 8 '19

Guess it pays to keep a beginner's mind. I've been using Ruby professionally for 7+ years and some of these were new to me.

Scott Tadman • May 8 '19 • Edited

They keep adding new toys to the language. One of my more recent discoveries is transform_keys and transform_values for Hash which they shipped without fanfare in Ruby 2.4. That's proven really valuable for "symbolizing" keys and cleaning up values.

Lenmor Ld • May 9 '19

Nice! As a beginner in Ruby, this is really helpful.
The thing that always trips me up is forgetting the | to surround the current element and using ( instead of {
I keep thinking like ES6 in Ruby 😳

Sahil • Jan 13 '20

Additional Bonus for you flatten. Flatten, as name suggests flatten out an array no matter how much nesting level is involved for an array. Below is the example for 3 level nesting

a =  [[1, 2, 3], [4, [5, [6, 7]]]]
b = a.flatten
# b = [1, 2, 3, 4, 5, 6, 7]

Also, you can do a.flatten!, which will overwrite a itself and assign the new value.

a =  [[1, 2, 3], [4, [5, [6, 7]]]]
a.flatten!
# a = [1, 2, 3, 4, 5, 6, 7]

Luke Duncan • May 8 '19 • Edited

Thanks for the awesome article Molly! I found it very helpful, the examples are clear and concise!

I've created a short cheatsheet on a Paper doc so people can keep it handy: paper.dropbox.com/doc/Ruby-Array-M...

Molly Struve (she/her) • May 8 '19

Wow, this is really fantastic! Thank you for putting that together. I will keep this in mind for future posts.

Do you mind if I add a link to your cheatsheet at the bottom of the post and share it on Twitter? I think people will find it very useful and I will definitely be sure to give you credit for it.

Luke Duncan • May 8 '19

Of course! After all, it is your work!!!

Jennifer Tran • May 8 '19

I've used some of these methods before but it was great to learn new ones such as detect and reject! I also never realized that some of these methods return the original array. Thank you for pointing that out and thank you for such a great tutorial!

Arit Developer • May 8 '19

What I LOVE about this tutorial, Molly, is how you include examples of how you used to code, before becoming proficient at these different methods. I laughed at each "newbie example" you gave, cos that's exactly how I've been doing things too! LOL. Thank you for this awesome resource!

Molly Struve (she/her) • May 8 '19

We all gotta start somewhere 😃

Lud • May 8 '19

For single methods without argument, you can use shorthand syntax (aka. "passing a proc"):

[1, 2, 3, 4].count(&:even?)
# => 2

Oliver • May 9 '19

You can also define your own methods and do something similar using &method.

def dog?(animal)
  ["spaniel", "schnauzer"].include? animal
end

["perch", "spaniel", "haddock", "schnauzer", "cod"].count(&method(:dog?))
#=> 2

Scott Tadman • May 8 '19

A lot of these convenience methods work on any Enumerator, and a lot of things emit those. You can even write your own with a few lines of code.

Molly Struve (she/her) • May 8 '19

YES! One of my favorite ruby methods currently is to_enum so you can use all these convenience methods with your own.

I originally had this post titled "Level Up Your Ruby Skillz: Working with Enumerators" but wanted to make it very approachable to new devs learning Ruby and figured starting with straight Arrays would be better.