Math helpers for collection

collection_math.rb

module CollectionMath

  class << self
  
    # Returns nil instead of 0 for an empty array
    def sum_values(collection)
      values = if block_given?
                 collection.map{ |item| yield item  }.compact
               else
                 collection
               end
      return nil if collection.empty?
      values.sum
    end
    
    # Average helper
    # Return nils for an empty array
    def average(collection)
      values = if block_given?
                 collection.map{ |item| yield item  }.compact
               else
                 collection
               end
      return nil if collection.empty?
      values.sum / values.size
    end

  end

end

It's better to raise custom errors, for example:

raise ArgumentError, "Empty value" if collection.empty?

Not for what I made that for. Rails will raise errors already. I need the values to be nil if not valid.