# Re: Isolating non-unique items in an array

**URL:** <https://www.ruby-forum.com/t/re-isolating-non-unique-items-in-an-array/72620>\
**Category:** Ruby\
**Created:** [October 18, 2006, 10:39am UTC](https://www.ruby-forum.com/t/re-isolating-non-unique-items-in-an-array/72620 "2006-10-18T10:39:22Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![phrogz](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/2acd7d/32.png) [@phrogz](https://www.ruby-forum.com/u/phrogz)\
**Post date:** [October 18, 2006, 10:39am UTC](https://www.ruby-forum.com/t/re-isolating-non-unique-items-in-an-array/72620/1 "2006-10-18T10:39:22Z")

</div>

From: Gavin K.

> But of course, other posts in this thread are likely faster.

How much faster? Much.

class Array  
def dcount1  
Hash[ \*uniq.map{ |e|  
if ( count = grep(e).size ) \> 1  
[e, count]  
end  
}.compact.flatten ]  
end

def dcount2  
inject( Hash.new(0) ){ |counts,e|  
counts[e]+=1  
counts  
}.reject{ |e,count|  
count==1  
}  
end

def dcount3  
counts = Hash.new(0)  
each{ |e| counts[e]+=1 }  
counts.reject{ |e,count| count==1 }  
end

end

a = %w| a a a a b c d d e b c f g h h i j k l l m n o p a b f h l m a a  
c d d b h l l m h |

runs = 10000  
require ‘benchmark’  
Benchmark.bmbm{ |x|  
x.report( ‘dcount1’ ){  
runs.times{ a.dcount1 }  
}  
x.report( ‘dcount2’ ){  
runs.times{ a.dcount2 }  
}  
x.report( ‘dcount3’ ){  
runs.times{ a.dcount3 }  
}  
}

#=\> user system total real  
#=\> dcount1 5.641000 0.000000 5.641000 ( 5.641000)  
#=\> dcount2 2.000000 0.015000 2.015000 ( 2.016000)  
#=\> dcount3 1.360000 0.016000 1.376000 ( 1.375000)