tests.rb

tests = {
  [1,1,1,1,0] => 0,
  [ 1, 1, 1, 2, 1, 1 ] => 2,
  [ 0, 0, 0.55, 0, 0 ] => 0.55
}

tests.each do |arr, expected|
  h = Hash.new(0)
  arr.each { |el| h[el] += 1 }
  p h.min_by { _2 }.first
end