Re: Algorithm for performing a rollup

From:
Chris <spam_me_not@goaway.com>
Newsgroups:
comp.lang.java.programmer
Date:
Sun, 18 Mar 2007 12:44:16 -0500
Message-ID:
<45fd7802$0$7463$9a6e19ea@news.newshosting.com>
Lew wrote:

Chris wrote:

Red Orchid wrote:

Chris <spam_me_not@goaway.com> wrote or quoted in
Message-ID: <45fc7346$0$7452$9a6e19ea@news.newshosting.com>:

input:
{"A", "A", "A", "B", "B", "C", "D", "D"}

output:
"A", 3
"B", 2
"C", 1
"D", 2


I'd push things into Collections.

public class Foo
{

  public static void main( String [] args )
  {
    List< String > starters =
      Arrays.asList( "A", "A", "A", "B", "B", "C", "D", "D" );

    Map< String, Integer > kounts = new HashMap< String, Integer >();
    for( String key : starters )
    {
      Integer k = kounts.get( key );
      kounts.put( key, Integer.valueOf(k == null? 1 : k + 1 ));
    }

    List< String > outters = new ArrayList< String >();
    outters.addAll( kounts.keySet() );
    Collections.sort( outters );

    for ( String key : outters )
    {
      System.out.println( "\""+ key + "\", "+ kounts.get( key ));
    }

  }

}


Thanks. This works, and has the advantage that it doesn't require the
input to be in order. The downside is that it isn't scalable. It needs
to store every unique element in memory. When you're processing very
large data sets, memory fills quickly.

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