How to Iterate Over Hash in Ruby: Syntax and Examples

In Ruby, you can iterate over a hash using the each method, which yields each key-value pair to a block. Use hash.each { |key, value| ... } to access keys and values inside the block.

Syntax

The basic syntax to iterate over a hash uses the each method. It passes two variables to the block: one for the key and one for the value.

• hash: your hash variable
• each: method to loop over each pair
• key, value: block variables representing each key and its value

ruby

hash.each do |key, value|
  # code using key and value
end

Example

This example shows how to print each key and value from a hash using each. It demonstrates accessing both parts of each pair.

ruby

person = { name: "Alice", age: 30, city: "New York" }
person.each do |key, value|
  puts "#{key}: #{value}"
end

Output

name: Alice
age: 30
city: New York

Common Pitfalls

One common mistake is using only one block variable, which will receive an array of [key, value] instead of separate variables. This can cause confusion when accessing keys or values.

Another pitfall is modifying the hash while iterating, which can lead to unexpected behavior.

ruby

hash = { a: 1, b: 2 }
hash.each do |pair|
  puts pair[0]  # key
  puts pair[1]  # value
end

# Better way:
hash.each do |key, value|
  puts key
  puts value
end

Output

a
1
b
2
a
1
b
2

Quick Reference

• each: iterate over key-value pairs
• each_key: iterate over keys only
• each_value: iterate over values only

Key Takeaways

Use each with two block variables to access keys and values separately.

Avoid using a single block variable unless you handle the key-value pair as an array.

Do not modify a hash while iterating over it to prevent errors.

Use each_key or each_value if you only need keys or values.

Iterating over hashes is simple and efficient with Ruby's built-in methods.