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Getting the index of an item in a sorted IList

By , 8 Dec 2011
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I wasn't going to publish this version, but I just used it a second time, so maybe someone else will need it too. This is very much like the second version above except that it uses a non-generic IList. Today, I used this to find and insert TreeNodes in a TreeNodeCollection, yesterday I used it with a ComboBox.Items.
 
public static bool TryGetIndex<T,U>
(
  this System.Collections.IList List
,
  T                             Sought
,
  Comparison<T,U>               Comparer
,
  out int                       Index
)
{
  bool result = false ;
 
  Index = 0 ;
 
  int lo = 0 ;
  int hi = List.Count - 1 ;
 
  while ( !result && ( lo <= hi ) )
  {
    Index = lo + ( hi - lo ) / 2 ;
 
    int diff = Comparer ( Sought , (U) List [ Index ] ) ;
 
    if ( diff == 0 )
    {
      result = true ;
    }
    else if ( diff < 0 )
    {
      hi = Index - 1 ;
    }
    else
    {
      lo = ++Index ;
    }
  }
 
  return ( result ) ;
}
 
Note that this is not as type-safe as when using the generic version. This hasn't caused me any trouble (yet) and you can add some protection if you encounter any problems.

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This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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PIEBALDconsult
Software Developer (Senior)
United States United States
BSCS 1992 Wentworth Institute of Technology
 
Originally from the Boston (MA) area. Lived in SoCal for a while. Now in the Phoenix (AZ) area.
 
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