Ruby: How to find item in array which has the most occurrences?

[1, 1, 1, 2, 3]
=> 1

['cat', 'dog', 'snake', 'dog']
=> dog

arr = [1, 1, 1, 2, 3]
freq = arr.inject(Hash.new(0)) { |h,v| h[v] += 1; h }
arr.sort_by { |v| freq[v] }.last

require 'benchmark'

class Array
  def mode1
    sort_by {|i| grep(i).length }.last
  end
  def mode2
    freq = inject(Hash.new(0)) { |h,v| h[v] += 1; h }
    sort_by { |v| freq[v] }.last
  end
  def mode3
    freq = inject(Hash.new(0)) { |h,v| h[v] += 1; h }
    max = freq.values.max                   # we're only interested in the key(s) with the highest frequency
    freq.select { |k, f| f == max }         # extract the keys that have the max frequency
  end
end

arr = Array.new(1_000) { |i| rand(100) }    # something to test with

Benchmark.bm(30) do |r|
  res = {}
  (1..3).each do |i|
    m = "mode#{i}"
    r.report(m) do
      100.times do
        res[m] = arr.send(m).inspect
      end
    end
  end
  res.each { |k, v| puts "%10s = %s" % [k, v] }
end

user     system      total        real
mode1                          34.375000   0.000000  34.375000 ( 34.393000)
mode2                           0.359000   0.000000   0.359000 (  0.359000)
mode3                           0.219000   0.000000   0.219000 (  0.219000)
     mode1 = 41
     mode2 = 41
     mode3 = [[41, 17], [80, 17], [72, 17]]

def mode4
  group_by{|i| i}.max{|x,y| x[1].length <=> y[1].length}[0]
end

==========================   IronRuby   =====================================
(iterations bumped to **1000**)    user     system      total        real
mode1 (I didn't bother :-))
mode2                           4.265625   0.046875   4.312500 (  4.203151)
mode3                           0.828125   0.000000   0.828125 (  0.781255)
mode4                           1.203125   0.000000   1.203125 (  1.062507)

class Array
    def mode4
      group_by{|i| i}.max{|x,y| x[1].length <=> y[1].length}[0]
    end
  end

user     system      total        real
mode1                          24.340000   0.070000  24.410000 ( 24.526991)
mode2                           0.200000   0.000000   0.200000 (  0.195348)
mode3                           0.120000   0.000000   0.120000 (  0.118200)
mode4                           0.050000   0.010000   0.060000 (  0.056315)
     mode1 = 76
     mode2 = 76
     mode3 = [[76, 18]]
     mode4 = 76

arr = [1, 1, 1, 2, 3]
arr.sort_by { |e| arr.grep(e).size }.last # => 1

class Array
  def mode
    sort_by {|i| grep(i).length }.last
  end
end

idx = {}
[2,2,1,3,1].each { |i| idx.include?(i) ? idx[i] += 1 : idx[i] = 1}

group_by { |n| n }.values.max_by(&:size).first

class Array
   def mode1
     group_by { |n| n }.values.max_by(&:size).first
   end
   def mode2
     freq = inject(Hash.new(0)) { |h,v| h[v] += 1; h }
     max = freq.values.max                   # we're only interested in the key(s) with the highest frequency
     freq.select { |k, f| f == max }         # extract the keys that have the max frequency
   end
end

arr = Array.new(1_0000) { |i| rand(100000) }    # something to test with

Benchmark.bm(30) do |r|
    (1..2).each do |i| r.report("mode#{i}") { 100.times do arr.send("mode#{i}").inspect; end }; end
end

user     system      total        real
mode1                           1.830000   0.010000   1.840000 (  1.876642)
mode2                           2.280000   0.010000   2.290000 (  2.382117)
 mode1 = 70099
 mode2 = [[70099, 3], [70102, 3], [51694, 3], [49685, 3], [38410, 3], [90815, 3], [30551, 3], [34720, 3], [58373, 3]]

def mode
  group_by {|x| x}.group_by {|k,v| v.size}.sort.last.last.map(&:first)
end