Each: The Unexpressive Enumerable

Learning Goal

• Use each to Work with an Array
• Explain why each is the least-expressive Enumerable

Introduction

In the previous lesson you learned that many of the Enumerable family are basically slight variations on map and reduce: all?, any?, etc.

But map and reduce are "child" Enumerables from the root Enumerable of them all, .each. In this lesson we'll talk about each.

Use each to Work with an Array

By now, you're so comfortable with Enumerables, you'll find .each follows the pattern of the "Character of Enumerable Methods."

oppressed_workers = ["Dopey", "Sneezy", "Happy", "Angry", "Doc", "Lemonjello", "Sleepy" ]
oppressed_workers.each do |oppressed_worker|
   puts "#{oppressed_worker.capitalize} wants to start a union!"
end #=>
# Dopey wants to start a union!
# Sneezy wants to start a union!
# Happy wants to start a union!
# Angry wants to start a union!
# Doc wants to start a union!
# Lemonjello wants to start a union!
# Sleepy wants to start a union!

We've saved talking about each for last. Despite the fact that each most simply expresses the "Character of Enumerable Methods," we're showing it last because we to use it least. Why is that?

Explain Why each is the Least-expressive Enumerable

We want to avoid each because it is the least-expressive Enumerable. It communicates the least to other programmers about what it is we're trying to do.

By now you recognize that map means: "create a new Array after transforming each element." You recognize that reduce means: "distill a value after joining elements together." These methods are expressive, their very nature tells other programmers what you intended to happen.

But what does each mean? Programmers, including you, recognize that map has a specific use, reduce has a specific use, max has a specific use. But each is generic. Are we just printing things, or are we trying to distill to a value, or are we trying to produce a transformed Array?

When we use each to do map things or reduce things we're not documenting what our intention was with regard to the collection. This makes for code that's harder to understand and debug. Here's some code that uses each instead of reduce.

def sum_array(number_array)
  total = 0
  number_array.each{ |num| total += num }
  total
end
sum_array([1,2,3]) #=> 6

Sure, it works, but it doesn't communicate. We should always strive to have code that communicates first and works second.

Identify Cases for each

The best time to use each is when you need to enumerate a collection but aren't transforming data. It's also great to use when you're not quite sure which Enumerable you want to use. The times when you're not better off map-ping or reduce-ing are few. The best use is to print out something to the screen:

oppressed_workers = ["Dopey", "Sneezy", "Happy", "Angry", "Doc", "Lemonjello", "Sleepy" ]
oppressed_workers.each do |oppressed_worker|
  puts "#{oppressed_worker.capitalize} wants to start a union!"
end

But on the other hand, you're probably just as good doing:

oppressed_workers = ["Dopey", "Sneezy", "Happy", "Angry", "Doc", "Lemonjello", "Undercaffinated" ]
angry_chants = oppressed_workers.map do |oppressed_worker|
  "#{oppressed_worker.capitalize} wants to start a union!"
end
p angry_chants

#=> ["Dopey wants to start a union!", "Sneezy wants to start a union!", "Happy wants to start a union!", "Angry wants to start a union!", "Doc wants to start a union!", "Lemonjello wants to start a union!", "Underrcaffinated wants to start a union!"]

List each Variants

The each method has a few close cousins that follow the "Character of Enumerable Methods." You want to recognize them, but you needn't memorize them. Consult the [Enumerables][enumdoc] documentation to see how the following work:

• each_cons
• each_entry
• each_slice
• each_with_index
• each_with_object (a cousin of reduce)

Conclusion

This concludes our discussion of each. It's the most flexible Enumerable, but it's also the least expressive. When you aren't sure which way to go, you might want to use it, but most of the time you really want to use map or reduce.