C# Implementation of SQL "Difference" and "Soundex"
By Anis Siddiqy |1 November 2015
Soundex is a phonetic algorithm for indexing names by sound, as pronounced in English. The goal is for homophones to be encoded to the same representation so that they can be matched despite minor differences in spelling.
This function will return the 4 character soundex of a given string.
public string Soundex(string data){
StringBuilder result = new StringBuilder();
if (data != null && data.Length > 0)
{
string previousCode, currentCode;
result.Append(Char.ToUpper(data[0]));
previousCode = string.Empty;
for (int i = 1; i < data.Length; i++)
{
currentCode = EncodeChar(data[i]);
if (currentCode != previousCode)
result.Append(currentCode);
if (result.Length == 4) break;
if (!currentCode.Equals(string.Empty))
previousCode = currentCode;
}
}
if (result.Length < 4)
result.Append(new String('0', 4 - result.Length));
return result.ToString();
}
private string EncodeChar(char c)
{
switch (Char.ToLower(c))
{
case 'b':
case 'f':
case 'p':
case 'v':
return "1";
case 'c':
case 'g':
case 'j':
case 'k':
case 'q':
case 's':
case 'x':
case 'z':
return "2";
case 'd':
case 't':
return "3";
case 'l':
return "4";
case 'm':
case 'n':
return "5";
case 'r':
return "6";
default:
return string.Empty;
}
}
The difference function will match the two soundex strings and return 0 to 4.
0 means Not Matched
4 means Strongly Matched
public int Difference(string data1, string data2)
{
int result = 0;
if (data1.Equals(string.Empty) || data2.Equals(string.Empty))
return 0;
string soundex1 = Soundex(data1);
string soundex2 = Soundex(data2);
if (soundex1.Equals(soundex2))
result = 4;
else
{
if (soundex1[0] == soundex2[0])
result = 1;
string sub1 = soundex1.Substring(1, 3); //characters 2, 3, 4
if (soundex2.IndexOf(sub1) > -1)
{
result += 3;
return result;
}
string sub2 = soundex1.Substring(2, 2); //characters 3, 4
if (soundex2.IndexOf(sub2) > -1)
{
result += 2;
return result;
}
string sub3 = soundex1.Substring(1, 2); //characters 2, 3
if (soundex2.IndexOf(sub3) > -1)
{
result += 2;
return result;
}
char sub4 = soundex1[1];
if (soundex2.IndexOf(sub4) > -1)
result++;
char sub5 = soundex1[2];
if (soundex2.IndexOf(sub5) > -1)
result++;
char sub6 = soundex1[3];
if (soundex2.IndexOf(sub6) > -1)
result++;
}
return result;
}