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Mapping values from two array in Ruby

Mapping values from two array in Ruby

"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."

Asked by: Guest | Views: 100
Total answers/comments: 4
Guest [Entry]

"@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(&:+)"
Guest [Entry]

"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 }"
Guest [Entry]

"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"
Guest [Entry]

"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)

For more details, see here or here."