How to Use Tally in Ruby: Count Elements Easily

In Ruby, tally is a method that counts how many times each element appears in an array or enumerable and returns a hash with elements as keys and counts as values. You simply call tally on an array or enumerable to get this count.

Syntax

The tally method is called on an array or any enumerable object. It returns a hash where each key is an element from the array, and the value is the number of times that element appears.

Syntax:

enumerable.tally

Here, enumerable can be an array or any enumerable object.

ruby

array = [1, 2, 2, 3, 3, 3]
counts = array.tally
puts counts

Output

{1=>1, 2=>2, 3=>3}

Example

This example shows how to use tally to count the frequency of words in an array.

ruby

words = ['apple', 'banana', 'apple', 'orange', 'banana', 'apple']
word_counts = words.tally
puts word_counts

Output

{"apple"=>3, "banana"=>2, "orange"=>1}

Common Pitfalls

One common mistake is trying to use tally on a hash or non-enumerable object, which will cause an error. Also, tally only works on Ruby 2.7 and later versions.

Another pitfall is expecting tally to sort the results; it does not sort the hash keys.

ruby

wrong = {a: 1, b: 2}
# wrong.tally # This will raise NoMethodError

# Correct usage:
array = [:a, :b, :a]
puts array.tally

Output

{:a=>2, :b=>1}

Quick Reference

Method	Description
tally	Counts occurrences of each element in an enumerable and returns a hash
tally { |item| block }	Counts occurrences based on the block's return value (Ruby 3.1+)
Works on arrays and enumerables	Only available in Ruby 2.7 and later

Key Takeaways

Use tally on arrays or enumerables to count element frequencies easily.

tally returns a hash with elements as keys and their counts as values.

tally requires Ruby 2.7 or newer to work.

It does not sort the results; sorting must be done separately if needed.

Avoid calling tally on non-enumerable objects like hashes.