How to Find the Sum of Array of Numbers in Ruby?

In Ruby 2.4+, you can calculate the sum of all numbers in an array using the Array#sum method, for example, in the following way:

# Ruby 2.4+
print [1, 2, 3, 4, 5].sum #=> 15
print [1.2, -4, 4.5, 3, 10].sum #=> 14.7
print [].sum #=> 0

It will throw a TypeError for non-numeric values (including numeric strings):

# Ruby 2.4+
# String can't be coerced into Integer (TypeError)
print ['foo', 1, 2, 3].sum

# String can't be coerced into Integer (TypeError)
print ['1', '2', '3', '4', '5'].sum

# nil can't be coerced into Integer (TypeError)
print [1, 2, 3, nil].sum

# ...

For versions of Ruby earlier than 2.4, you can use the Enumerable#inject method (or its alias Enumerable#reduce) instead, in the following way:

array.inject(0) { | sum, n | sum + n }

Passing 0 as the initial operand (or base case) is important as nil would be returned for empty arrays otherwise.

You may shorten this using the following syntax:

array.inject(0, :+)

This follows the following method signature for Enumerable#inject (where + is passed as a symbol to the method):

# inject(initial, symbol) → obj

For example:

def sum(numbers)
    numbers.inject(0, :+)
end

print sum([1, 2, 3, 4, 5]) #=> 15
print sum([1.2, -4, 4.5, 3, 10]) #=> 14.7
print sum([]) #=> 0

It will throw a TypeError for non-numeric values (including numeric strings):

# String can't be coerced into Integer (TypeError)
print sum(['foo', 1, 2, 3])

# String can't be coerced into Integer (TypeError)
print sum(['1', '2', '3', '4', '5'])

# nil can't be coerced into Integer (TypeError)
print sum([1, 2, 3, nil])

# ...