How to Use sum in Ruby: Simple Guide with Examples

In Ruby, you can use the sum method to add all elements of an array or range. Simply call sum on the collection, like [1, 2, 3].sum, which returns 6. You can also provide a starting value or a block for custom summing.

Syntax

The sum method is called on an Enumerable like an array or range. It can be used in two main ways:

• collection.sum - adds all elements starting from zero.
• collection.sum(initial) - starts adding from the initial value.
• collection.sum(initial) { |element| block } - sums the result of the block applied to each element.

This method returns the total sum as a number.

ruby

array.sum
array.sum(10)
array.sum(0) { |x| x * 2 }

Example

This example shows how to sum numbers in an array, use a starting value, and sum squares of numbers using a block.

ruby

numbers = [1, 2, 3, 4, 5]

# Sum all elements
puts numbers.sum

# Sum with a starting value
puts numbers.sum(10)

# Sum squares of elements
puts numbers.sum(0) { |n| n * n }

Output

15
25
55

Common Pitfalls

Some common mistakes when using sum include:

• Calling sum on an empty array without an initial value returns 0, which is expected but sometimes surprising.
• Using sum on arrays with non-numeric elements without a block will cause errors.
• For older Ruby versions (before 2.4), sum is not available by default.

ruby

wrong = ['a', 'b', 'c']
# wrong.sum # This will raise an error

# Correct way with block:
correct = ['a', 'b', 'c']
puts correct.sum('') { |s| s.upcase }

Output

ABC

Quick Reference

Usage	Description	Example
collection.sum	Sum all elements starting at 0	[1,2,3].sum #=> 6
collection.sum(initial)	Sum starting at initial value	[1,2,3].sum(10) #=> 16
collection.sum(initial) { |e| block }	Sum results of block starting at initial	[1,2,3].sum(0) { |n| n*2 } #=> 12

Key Takeaways

Use sum to add all elements in arrays or ranges easily.

You can provide a starting value to sum to begin adding from that number.

Use a block with sum to customize what gets added for each element.

Calling sum on non-numeric arrays without a block causes errors.

The sum method is available in Ruby 2.4 and later versions.