map

If you want to use the processing map method see methods map1d

map and map! in ruby

Example: creating an array from range using map and a block

(0..8).map { rand(0..8) }

Example: creating a random array of Cube objects from range using map and a block

@cubies = (0..CUBE_NO).map { Cube.new(rand(5..15)) }

Example: creating an array Vec3D from an array of numbers using map and a block

@arr = [0, 0.5, 1.5, 3.5, 7.5, 15].map { |x| Vec3D.new(x * -1, x, x * -1) }

NB: if no block is given an enumerator is returned instead (see map documentation)

Subtleties

Say there is an array this class Foo (it is usually Foo unless it is Bar or FooBar)

class Foo
  def method_name
    puts "method called for #{object_id}"
  end
end

Now we want iterate of the array calling the method_name on each element, we could use map and a block as below:-

[Foo.new, Foo.new].map do |element|
  element.method_name
end

# => method called for 70339841711300
# => method called for 70339841711280

However ruby there are often shortcuts, here is one example where the shortform version would be preferred (since it is a common ruby idiom):-

[Foo.new, Foo.new].map(&:method_name)

The & takes the operand :method_name and turns it into a Proc (unless it is already a Proc) and passes it as if a block had been called. The result is that two forms produce the same result.