How do I get the unique elements from an array of hashes in Ruby?

a = [{:a => 1},{:a => 2}, {:a => 1}]
a.uniq # => [{:a => 1}, {:a => 2}, {:a => 1}]

[{:a => 1}, {:a => 2}]

a = [{:a => 1},{:a => 2}, {:a => 1}]
a.inject([]) { |result,h| result << h unless result.include?(h); result }

[{:a=>1}, {:a=>2}]

[{:x=>1},{:x=>2},{:x=>3},{:x=>2},{:x=>1}]

[{:x=>1}, {:x=>1}, {:x=>2}, {:x=>2}, {:x=>3}]

your_array.inject([]) do |result,item|
  result << item if !result.last||result.last[:x]!=item[:x]
  result
end

test.inject([]) {|r,h| r<<h unless r.find {|t| t[:x]==h[:x]}; r}.sort_by {|t| t[:x]}

test=[]
1000.times {test<<{:x=>rand}}

Benchmark.bmbm do |bm|
  bm.report("sorting: ") do
    test.sort_by {|t| t[:x]}.inject([]) {|r,h| r<<h if !r.last||r.last[:x]!=h[:x]; r}
  end
  bm.report("inject: ") {test.inject([]) {|r,h| r<<h unless r.find {|t| t[:x]==h[:x]}; r}.sort_by {|t| t[:x]} }
end

Rehearsal ---------------------------------------------
sorting:    0.010000   0.000000   0.010000 (  0.005633)
inject:     0.470000   0.140000   0.610000 (  0.621973)
------------------------------------ total: 0.620000sec

                user     system      total        real
sorting:    0.010000   0.000000   0.010000 (  0.003839)
inject:     0.480000   0.130000   0.610000 (  0.612438)

[{:a=>1}, {:a=>2}, {:a=>1}].uniq
#=> [{:a=>1}, {:a=>2}]

a.map {|h| h.to_a[0]}.uniq.map {|k,v| {k => v}}

[[:a, 1], [:a, 2], [:a, 1]]

[[:a, 1], [:a, 2]]