Getting the least common multiple of an array of integers in Ruby

I know that, in Ruby, you can use the [`Integer#lcm`](

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) method to get the least common multiple of two numbers. For example:

10.lcm(15)
# => 30

Is there an efficient (or built-in to the core or stdlib) way to get the least common multiple of all the integers in a given array? For example:

[5, 3, 10, 2, 20].lcm
# => 60

[5,3,10,2,20].reduce(&:lcm)

Any operation that takes two operands can be applied iteratively to a collection by [folding][1] it: [Enumerable#inject/reduce][2]. To cover the empty case, pass as first argument the [identity element][3] of the operation, which is `1` for the least common denominator.

[5, 3, 10, 2, 20].reduce(1) { |acc, n| acc.lcm(n) } # => 60

Which can be also written as:

[5, 3, 10, 2, 20].reduce(1, :lcm)


[1]:

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[2]:

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[3]:

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In addition to tokland's answer, if you really want an `#lcm` method to act on an _array of integers_, you could add an instance method to the Array class.

```lang-ruby
class Array
def lcm
self.reduce(1, :lcm)
end
end

puts 10.lcm(15)
# => 30
puts [5,3,10,2,20].lcm
# => 60
```

(This practice is called [Monkey patching][1], as you're extending a class at runtime. Some people do frown upon the practice though.)

[1]:

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