# Re: can this code be improved

From:
ram@zedat.fu-berlin.de (Stefan Ram)
Newsgroups:
comp.lang.java.programmer
Date:
17 Aug 2006 01:10:02 GMT
Message-ID:
<map-bug-20060817030500@ram.dialup.fu-berlin.de>
ram@zedat.fu-berlin.de (Stefan Ram) writes:

sort.put( -map.get( i ), i );

This attempt to "invert" a map still has a bug: If two keys of
the original map have the same value, one of them will be
lost. The following solution uses a small "bias" added to
each value, to make it different from every other value.
(It might fail under some conditions.)

class NumericMapUtils
{ public static <D> void addTo
( final java.util.Map<D,java.lang.Integer> map, final D d, final int i )
{ map.put( d, i +( map.containsKey( d )? map.get( d ): 0 )); }}

public class Main
{ static final java.util.Random rand = new java.util.Random();
public static void main( java.lang.String[] args )
{ final java.util.Map<java.lang.Integer,java.lang.Integer> map
= new java.util.HashMap<java.lang.Integer,java.lang.Integer>( 50 );
final int k = 1000; for( int i = 0; i < k; ++i )
NumericMapUtils.<java.lang.Integer>addTo( map, rand.nextInt( 49 ), 1 );
final java.util.SortedMap<java.lang.Double,java.lang.Integer> sort
= new java.util.TreeMap<java.lang.Double,java.lang.Integer>();
int j = 0; for( final java.lang.Integer i : map.keySet() )
sort.put( -map.get( i )+ j++ * .8 / k, i );
int c = 0; for( final java.lang.Double d : sort.keySet() )
{ java.lang.System.out.println
( "Rank " +( c + 1 )+ " number is " + sort.get( d ));
if( ++c >= 6 )break; }}}

A more clean solution might replace each key of the map
"sort" by a ComparablePair of both the key and its value.

I even have implemented such a beast

http://www.purl.org/stefan_ram/html/ram.jar/de/dclj/ram/type/pair/ComparablePair.html

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