gistfile1.txt

@ores = [
  {name: 'foo', cost: 100},
  {name: 'bar', cost: 100},
  {name: 'foo', cost: 100},
  {name: 'baz', cost: 100},
  {name: 'bar', cost: 100}
]


@ores.select { |o| o['name'] == 'foo' } => [{name: 'foo', cost: 100}, {name: 'foo', cost: 100}]
@ores.select { |o| o['name'] == 'foo' }.map { |o| o['cost'] } => [100, 100]
@ores.select { |o| o['name'] == 'foo' }.map { |o| o['cost'] }.reduce(&:+) => 200