Question

I have an array of arrays in Ruby:

price_list = [
  ['Brand-1', 'Model-1', 100.00],
  ['Brand-1', 'Model-2', 200.00],
  ['Brand-2', 'Model-1', 10.00],
  ['Brand-2', 'Model-2', 20.00],
  ['Brand-1', 'Model-1', 110.00],
  ['Brand-1', 'Model-2', 190.00],
  ['Brand-1', 'Model-3', 300.00],
  ...
  ['Brand-n', 'Model-n', 1234.00]
]

And I need to create new array with only unique products and minimal prices. Something like this:

new_price_list = [
  ['Brand-1', 'Model-1', 100.00],
  ['Brand-2', 'Model-1', 10.00],
  ['Brand-2', 'Model-2', 20.00],
  ['Brand-1', 'Model-2', 190.00],
  ['Brand-1', 'Model-3', 300.00],
  ...
  ['Brand-n', 'Model-n', 1234.00]
]

What is a fastest and most beautiful way to do this in Ruby?

Answer 1

Group by key (brand+model) and then get the minimum price on the grouped arrays:

prices = [
  ['Brand-1', 'Model-1', 100.00],
  ['Brand-1', 'Model-2', 200.00],
  ['Brand-2', 'Model-1', 10.00],
  ['Brand-2', 'Model-2', 20.00],
  ['Brand-1', 'Model-1', 110.00],
  ['Brand-1', 'Model-2', 190.00],
  ['Brand-1', 'Model-3', 300.00],
]

grouped = prices.group_by { |brand, model, price| [brand, model] }
grouped.values.map { |grouped_prices| grouped_prices.min_by(&:last) }

Output:

[["Brand-1", "Model-2", 190.0],
 ["Brand-1", "Model-3", 300.0],
 ["Brand-2", "Model-1", 10.0],
 ["Brand-2", "Model-2", 20.0],
 ["Brand-1", "Model-1", 100.0]]