How to sum array of numbers in Ruby?

Summing elements of an array is one of the most common operations in Ruby. Whether you’re tallying up numeric values for a simple script or doing more advanced data processing, Ruby provides multiple ways to get the job done. Below, we’ll look at three main approaches:

1. The sum method (Ruby 2.4+)
2. inject (or reduce)
3. ActiveSupport’s sum in Rails (Pre-Ruby 2.4)

1. Using the Built-in sum Method (Ruby 2.4+)

As of Ruby 2.4, arrays have a built-in method sum, making summation straightforward:

numbers = [1, 2, 3, 4, 5]
total = numbers.sum
puts total  # => 15

Why Use sum?

• Readability: numbers.sum clearly communicates your intention.
• Options: You can provide an initial value if needed:

  total = numbers.sum(100)  # => 115

• Performance: Under the hood, it’s implemented efficiently in C for MRI (Matz’s Ruby Interpreter).

2. Using inject (or reduce)

If you’re on older Ruby versions (pre-2.4) or want a more functional style, you can use inject or reduce:

numbers = [1, 2, 3, 4, 5]
total = numbers.inject(0) { |sum, n| sum + n }
puts total  # => 15

Or equivalently:

total = numbers.reduce(:+)

How It Works

• inject(0) sets the initial sum to 0.
• Block Variables: The first block parameter (sum) accumulates the result, while the second (n) is each element in the array.
• Symbol Shortcut: reduce(:+) tells Ruby to apply the + operation between elements, implicitly starting with the first element.

3. In Rails Projects (Pre-Ruby 2.4): ActiveSupport’s sum

Before Ruby 2.4 introduced the native Array#sum, many Rails applications used ActiveSupport’s sum method:

numbers = [1, 2, 3, 4, 5]
total = numbers.sum
puts total  # => 15

If you’re working in a modern Rails environment, you can safely use sum directly on arrays. But keep in mind that in older Rails versions, Array#sum was part of ActiveSupport, not core Ruby.

Edge Cases and Considerations

1. Empty Arrays
   • [].sum returns 0.
   • [].inject(0) also returns 0.
2. Mixed Data Types
   • Ensure your array contains only numeric values or objects that respond to +. Otherwise, you may encounter a TypeError.
3. Performance
   • For large arrays, sum is typically quite efficient. But if you need more complex operations, consider enumerator laziness (via Enumerator or external libraries) to optimize resource usage.

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Conclusion

To sum an array of numbers in Ruby, you can:

1. Use sum (Ruby 2.4+), the most straightforward and readable method.
2. Use inject or reduce if you’re on an older Ruby version or prefer a functional style.
3. Use ActiveSupport’s sum in Rails environments (pre-Ruby 2.4), which provides similar functionality.

By choosing the method that best fits your Ruby or Rails version—and applying good coding practices—you’ll have no trouble handling sums in your Ruby applications.