Enumerable operates at it's core using the each method. When you call map, map is using each.
[1,2,3].map { |n| n ** 2 }
[1,2,3].collect { |n| n ** 2 }
# => [1, 4, 9]
[1,3,6,3,2,346,6,7].sort
# => [1, 2, 3, 3, 6, 6, 7, 346]
alphabetical_products = Product.all.sort_by {|product| product.name }
alphabetical_products.first
# => #<Product:0x007fc599d8f390 @id=5943, @name="Afraid Apples", @vendor_id=1958>
[1,2,4].max
# => 4
[1,2,4].min
# => 1
Sale.all.min_by { |sale| sale.amount }
Sale.all.max_by { |sale| sale.amount }
Sale.all.sort_by { |sale| sale.amount }.first(5)
# Returns the 5 sales with the lowest amount
Product.all.group_by {|product| product.name.split.last }
# Returns a hash, the keys being the name of the food type, the values being an array of products.
[1,2,3,4].find {|n| n < 3 }
# => 1[1,2,3,4].find_all {|n| n < 3 }
# => [1,2]