Difference of max and max_by in Ruby

array.rb

array = [
  { id: 1, lv: 56 },
  { id: 2, lv: 12 },
  { id: 3, lv: 38 },
  { id: 4, lv: 99 },
  { id: 5, lv: 27 },
]
p array.max { |a, b| a[:lv] <=> b[:lv] } # => {:id:4, lv:99}
p array.max_by { |v| v[:lv] }            # => {:id:4, lv:99}

hash.rb

hash = {
  a: { id: 1, lv: 56 },
  b: { id: 2, lv: 12 },
  c: { id: 3, lv: 38 },
  d: { id: 4, lv: 99 },
  e: { id: 5, lv: 27 },
}
p hash.max { |(k1, v1), (k2, v2)| v1[:lv] <=> v2[:lv] } # => [:d, {:id=>4, :lv=>99}]
p hash.max_by { |(k, v)| v[:lv] }                     # => [:d, {:id=>4, :lv=>99}]