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Things We Can Do with Hashes

Things We Can Do with Hashes

Practice calling some important methods on hashes.

We'll cover the following...

Methods of the Hash class

The main purpose of a Hash object is to look a value up by a key. However, there are a few more things we can do with hashes. Below is a list of methods supported by the Hash class. Don’t be too concerned with memorizing all of them.

The merge method

We can merge two hashes by calling the merge method:

Ruby
dictionary={ "one" => "eins" }.merge({ "two" => "zwei" })
puts dictionary

The fetch method

The fetch method does just the same as the square bracket lookup ([]) discussed before, but it raises an error if the key isn’t defined:

Ruby
dictionary = { "one" => "eins" }
puts dictionary.fetch("one")
puts dictionary.fetch("two")

Notice that line 2 outputs “eins”, but line 3 raises an error.

The keys method

The keys method returns an array with all the keys that the hash knows:

Ruby
dictionary = { "one" => "eins", "two" => "zwei" }
puts dictionary.keys

The length and size methods

The length and size methods both indicate the number of key/value pairs contained in the hash:

Ruby
dictionary = { "one" => "eins", "two" => "zwei" }
puts dictionary.length
puts dictionary.size