Hash#each

hash.each { |key, value| block } -> hash

The Hash class provides three primary methods for iterating over key-value pairs: .each, .each_pair, and .each_with_object. Each serves a slightly different purpose depending on whether you need to modify the hash during iteration or accumulate a result in a separate object.

.each

The .each method iterates over each key-value pair and yields both to the block. It returns the original hash, making it chainable with other methods.

user = { name: "Alice", age: 30, city: "London" }

user.each do |key, value|
  puts "#{key}: #{value}"
end
# Output:
# name: Alice
# age: 30
# city: London

You can also iterate over just keys or just values:

user.each_key { |key| puts key }
# name
# age
# city

user.each_value { |value| puts value }
# Alice
# 30
# London

.each_pair

The .each_pair method is identical to .each. Both iterate over key-value pairs and return the hash. Ruby provides both as aliases, though .each is more commonly used.

config = { theme: "dark", font_size: 14, auto_save: true }

config.each_pair do |key, value|
  puts "#{key} = #{value}"
end

.each_with_object

The .each_with_object method differs significantly from .each and .each_pair. It takes an object as an argument and yields that object along with each key-value pair. The object persists across iterations and is returned at the end. This makes it useful for accumulating results without explicitly tracking external variables.

numbers = { a: 1, b: 2, c: 3, d: 4 }

sum = numbers.each_with_object(0) do |(key, value), accumulator|
  accumulator + value
end

puts sum  # => 10

Notice the destructuring syntax — you can unpack the key-value pair directly in the block parameters.

You can build arrays, hashes, or any object:

words = { first: "hello", second: "world", third: "ruby" }

uppercased = words.each_with_object({}) do |(key, value), result|
  result[key] = value.upcase
end

# => { first: "HELLO", second: "WORLD", third: "RUBY" }

Choosing the Right Method

Use .each or .each_pair when you need to:

• Perform side effects (printing, logging)
• Chain methods on the hash itself
• Iterate without needing to accumulate a result

Use .each_with_object when you need to:

• Build a new data structure from the hash
• Avoid explicit variable mutation outside the block
• Create transformations in a functional style

Ruby Version Notes

All three methods are available in Ruby 1.8 and later. The destructuring syntax requires Ruby 2.7 or later. Ruby 3.x maintains full backward compatibility.

See Also

• hash-dig — Safely retrieve nested values
• hash-dig — Returns key-value array or nil