This is a simple category on NSString to allow comparisons using the Soundex algorithm. This compares a string by the way it sounds, i.e. phonetically. It can be quite handy for suggesting alternative words for example, or doing fuzzy matches, book indexing, etc. GrahamCox.

#import <Cocoa/Cocoa.h>

@interface NSString (Soundex)

• (NSString*) soundexString;
• (BOOL) soundsLikeString:(NSString*) aString;

@end

#import “NSString+Soundex.h”

@implementation NSString (Soundex)

static NSArray* soundexCharSets = nil;

• (void) initSoundex { if( soundexCharSets == nil ) { NSMutableArray* cs = [NSMutableArray array]; NSCharacterSet* charSet;

    charSet = [NSCharacterSet characterSetWithCharactersInString:@"aeiouhw"];
    [cs addObject:charSet];
    charSet = [NSCharacterSet characterSetWithCharactersInString:@"bfpv"];
    [cs addObject:charSet];
    charSet = [NSCharacterSet characterSetWithCharactersInString:@"cgjkqsxz"];
    [cs addObject:charSet];
    charSet = [NSCharacterSet characterSetWithCharactersInString:@"dt"];
    [cs addObject:charSet];
    charSet = [NSCharacterSet characterSetWithCharactersInString:@"l"];
    [cs addObject:charSet];
    charSet = [NSCharacterSet characterSetWithCharactersInString:@"mn"];
    [cs addObject:charSet];
    charSet = [NSCharacterSet characterSetWithCharactersInString:@"r"];
    [cs addObject:charSet];
  	
    soundexCharSets = [cs retain];   } }
  

• (NSString ) stringByRemovingCharactersInSet:(NSCharacterSet) charSet options:(unsigned) mask { NSRange range; NSMutableString* newString = [NSMutableString string]; unsigned len = [self length];

  mask &= ~NSBackwardsSearch; range = NSMakeRange (0, len); while (range.length) { NSRange substringRange; unsigned pos = range.location;

    range = [self rangeOfCharacterFromSet:charSet options:mask range:range];
    if (range.location == NSNotFound)
        range = NSMakeRange (len, 0);
  	
    substringRange = NSMakeRange (pos, range.location - pos);
    [newString appendString:[self substringWithRange:substringRange]];
  	
    range.location += range.length;
    range.length = len - range.location;   }
  

  return newString; }

• (NSString ) stringByRemovingCharactersInSet:(NSCharacterSet) charSet { return [self stringByRemovingCharactersInSet:charSet options:0]; }

• (unsigned) soundexValueForCharacter:(unichar) aCharacter { // returns the soundex mapping for the first character in the string. If the value returned is 0, the character should be discarded.

  unsigned indx; NSCharacterSet* cs;

  for( indx = 0; indx < [soundexCharSets count]; ++indx ) { cs = [soundexCharSets objectAtIndex:indx];

    if([cs characterIsMember:aCharacter])
        return indx;   }
  

  return 0; }

• (NSString) soundexString { // returns the Soundex representation of the string. /

  Replace consonants with digits as follows (but do not change the first letter): b, f, p, v => 1 c, g, j, k, q, s, x, z => 2 d, t => 3 l => 4 m, n => 5 r => 6 Collapse adjacent identical digits into a single digit of that value. Remove all non-digits after the first letter. Return the starting letter and the first three remaining digits. If needed, append zeroes to make it a letter and three digits.

  */

  [self initSoundex];

  if([self length] > 0) { NSMutableString* soundexStr = [NSMutableString string];

    // strip whitespace and convert to lower case
  	
    NSString*	workingString = self lowercaseString] stringByRemovingCharactersInSet:[[[NSCharacterSet whitespaceAndNewlineCharacterSet]];
    unsigned	indx, soundValue, previousSoundValue = 0;
  	
    // include first character
  	
    [soundexStr appendString:[workingString substringToIndex:1]];
  	
    // convert up to 3 more significant characters
  	
    for( indx = 1; indx < [workingString length]; ++indx )
    {
        soundValue = [self soundexValueForCharacter:[workingString characterAtIndex:indx]];
  		
        if( soundValue > 0 && soundValue != previousSoundValue )
            [soundexStr appendString:[NSString stringWithFormat:@"%d", soundValue]];
  			
        previousSoundValue = soundValue;	
  		
        // if we've got four characters, don't need to scan any more
  		
        if([soundexStr length] >= 4)
            break;
    }
  	
    // if < 4 characters, need to pad the string with zeroes
  	
    while([soundexStr length] < 4)
        [soundexStr appendString:@"0"];
  	
    //NSLog(@"soundex for '%@' = %@", self, soundexStr );
  	
    return soundexStr;   }   else
    return @""; }
  

• (BOOL) soundsLikeString:(NSString*) aString { return self soundexString] isEqualToString:[aString soundexString; }

@end