I'm wondering if there's a way to do what I can do below with Python, in Ruby:
sum = reduce(lambda x, y: x + y, map(lambda x, y: x * y, weights, data))
I have two arrays of equal sizes with the weights and data but I can't seem to find a function similar to map in Ruby, reduce I have working.
@Michiel de Mare
Your Ruby 1.9 example can be shortened a bit further:
weights.zip(data).map(:*).reduce(:+)
Also note that in Ruby 1.8, if you require ActiveSupport (from Rails) you can use:
weights.zip(data).map(&:*).reduce(&:+)
[1,2,3].zip([4,5,6]).map(:*)
weights.zip(data).sum { |s,d| s*d }.In Ruby 1.9:
weights.zip(data).map{|a,b| a*b}.reduce(:+)
In Ruby 1.8:
weights.zip(data).inject(0) {|sum,(w,d)| sum + w*d }
The Array.zip function does an elementwise combination of arrays. It's not quite as clean as the Python syntax, but here's one approach you could use:
weights = [1, 2, 3]
data = [4, 5, 6]
result = Array.new
a.zip(b) { |x, y| result << x * y } # For just the one operation
sum = 0
a.zip(b) { |x, y| sum += x * y } # For both operations
Ruby has a map method (a.k.a. the collect method), which can be applied to any Enumerable object. If numbers is an array of numbers, the following line in Ruby:
numbers.map{|x| x + 5}
is the equivalent of the following line in Python:
map(lambda x: x + 5, numbers)
weights = [1,2,3]
data = [10,50,30]
require 'matrix'
Vector[*weights].inner_product Vector[*data] # => 200
An alternative for the map that works for more than 2 arrays as well:
def dot(*arrays)
arrays.transpose.map {|vals| yield vals}
end
dot(weights,data) {|a,b| a*b}
# OR, if you have a third array
dot(weights,data,offsets) {|a,b,c| (a*b)+c}
This could also be added to Array:
class Array
def dot
self.transpose.map{|vals| yield vals}
end
end
[weights,data].dot {|a,b| a*b}
#OR
[weights,data,offsets].dot {|a,b,c| (a*b)+c}
