drop Archives : Global Nerdy

Enumerating Enumerable marches on!

This is the seventh article in my series in which I try to do a better job of documenting Ruby’s Enumerable module than Ruby-Doc.org does. If you’ve missed the other articles in the series, they’re listed below:

In this installment, I cover a method added in Ruby 1.9: drop.

Enumerable#drop Quick Summary

$Graphic representation of the \"drop\" method in Ruby\'s \"Enumerable\" module$

In the simplest possible terms	Given a collection and a number n, create an array made of the items of the collection with the first n items removed.
Ruby version	1.9 only
Expects	The number of elements to remove from the start of the collection.
Returns	An array made up of the remaining items, if there are any./td>
RubyDoc.org’s entry	Enumerable#drop

Enumerable#drop and Arrays

With an array, drop takes a number n as an argument and returns an array created by removing the first n elements of the array. The resulting array is made up of the remaining elements.


# These are the favourite bands of RubyFringe organizer
# Meghan Katleen Millard's, according to her Facebook profile
meghans_fave_bands = ["Afghan Whigs", "Bjork", "Charles Mingus",
"Deerhunter", "Electrelane", "Francois Hardy", "Godspeed You Black Emperor!"]
=> ["Afghan Whigs", "Bjork", "Charles Mingus", "Deerhunter", "Electrelane",
"Francois Hardy", "Godspeed You Black Emperor!"]

# Let's lose the first 5
meghans_fave_bands.drop 5
=> ["Francois Hardy", "Godspeed You Black Emperor!"]

# The original array is not affected
meghans_fave_bands
=> ["Afghan Whigs", "Bjork", "Charles Mingus", "Deerhunter", "Electrelane",
"Francois Hardy", "Godspeed You Black Emperor!"]

Enumerable#drop and Hashes

With an hash, drop takes a number n as an argument and returns an array created by removing the first n elements of the array (drop is only in Ruby 1.9 and later, where hashes keep the order in which they were defined, so its results are predictable). The resulting array is made up of the remaining elements, with each element converted into a two-element array where element 0 is the key and element 1 is the corresponding value.


# Here's a hash of the first five U.S. states
# (in terms of alphabetical order) and their capitals.
# This example is in Ruby 1.9, which means that
# the hash keys will stay in the order in which
# they were defined.
states_and_capitals = {"Alabama" => "Montgomery", \
                       "Alaska"  => "Juneau", \
                       "Arizona" => "Phoenix", \
                       "Arkansas" => "Little Rock", \
                       "California" => "Sacramento"}
=> {"Alabama"=>"Montgomery", "Alaska"=>"Juneau", "Arizona"=>"Phoenix",
"Arkansas"=>"Little Rock", "California"=>"Sacramento"}

# Let's remove the first 3
states_and_capitals.drop 3
=> [["Arkansas", "Little Rock"], ["California", "Sacramento"]]

# The original hash is not affected
states_and_capitals
=> {"Alabama"=>"Montgomery", "Alaska"=>"Juneau", "Arizona"=>"Phoenix",
"Arkansas"=>"Little Rock", "California"=>"Sacramento"}

Enumerable#take: Enumerable#drop’s Evil Twin

I’ll cover take in detail in a later installment, but for now, an example should suffice:


meghans_fave_bands = ["Afghan Whigs", "Bjork", "Charles Mingus",
"Deerhunter", "Electrelane", "Francois Hardy", "Godspeed You Black Emperor!"]
=> ["Afghan Whigs", "Bjork", "Charles Mingus", "Deerhunter", "Electrelane",
"Francois Hardy", "Godspeed You Black Emperor!"]

# drop(n) removes the first n elements
meghans_fave_bands.drop(4)
=> ["Electrelane", "Francois Hardy", "Godspeed You Black Emperor!"]

meghans_fave_bands.take(4)
=> ["Afghan Whigs", "Bjork", "Charles Mingus", "Deerhunter"]