How can i find repeated words in a string in c#?

Question

1.93/5 (4 votes)

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Hi,

i have sequence of characters immediately followed by the same sequence then i want the program to remove the repeated words like the string 'abcdabcd' i need abcd

how can i do that.

Thanks inadvance

Posted 16-May-13 3:02am

pradeep manne

Updated 16-May-13 3:06am

Zoltán Zörgő

v2

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Comments

Nani Babu 16-May-13 9:30am

I have one query, In above string "abcdabcd" : 'abc', 'ab' ,'bc' also repeated. On what basis you want repeated words? (length or what)

pradeep manne 16-May-13 10:21am

hi ,
thanks for the replay
in the string"abcdabcd" i need the repeated word
like"repeatedrepeated" i need only one word "repeated"

Walby 16-May-13 10:43am

Hi pradeep manne, do you know the phrase you are looking for in the string, that is repeated, or is it all repeated words in a string. i.e. "abcdabcd" return "ab" and "cd".

3 solutions

Solution 1

If string has only one word repeated twice then you can try below

C#

string str = "abcdabcd";
string temp = str.Substring(0, str.Length / 2);

Posted 16-May-13 3:38am

CrystalB

Solution 2

I am making some assumptions on what you are looking for (your question isn't entirely clear) but I think this does the trick.

You can use a System.Text.StringBuilder and then split the original string using the built up string. Once you have all of the parsed items as string empty that is your repeated string and you break out of the loop.

C#

string val = "abcabcabc";
System.Text.StringBuilder sb = new System.Text.StringBuilder();
string result = string.Empty;
foreach (var c in val)
{
   sb.Append(c);
   var parsed = val.Split(new string[] {sb.ToString()}, StringSplitOptions.None);
   var stringFound = !parsed.Any(s => s != string.Empty);//All items are empty
   
   if (stringFound)
   {
      result = sb.ToString();
      break;
   }
}

After this runs your string that is repeated will be in result. Note the algorithm breaks out after the first occurance because it will also meet the criteria when the sb contains all characters of the original string. This algorithm will find any number of it being repeated but assumes the string only contains the repeated sequence.

Posted 16-May-13 5:24am

N_tro_P

Updated 16-May-13 5:34am

v5

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Matt T Heffron · Accepted Answer · 2013-05-16T06:40:00

Regex is your friend!

C#

using System;
using System.Diagnostics;
using System.Text.RegularExpressions;
namespace ConsoleApplication16
{
  class Program
  {
    static readonly string[] Tests = { "abcdabcd", "xabcdabcd", "abcdabc", "xaaabcdabcd" };
    static readonly Regex FindDup = new Regex(@"(.+)\1", RegexOptions.IgnoreCase);
    static void Main(string[] args)
    {
      foreach (string t in Tests)
      {
        MatchCollection allMatches = FindDup.Matches(t);
        Trace.WriteLine(string.Format("{0}: {1}", t, allMatches.Count));
      }
    }
  }
}

Results:

abcdabcd: 1
xabcdabcd: 1
abcdabc: 0
xaaabcdabcd: 2

This will also identify what the matching strings are, in the allMatches collection.

EDIT: Add response to Collin's comments:
Each of the Match values in the allMatches contains the information about the doubled text in the Groups property. Groups[0] contains the whole matched string (both copies), and Groups[1] contains the string of the single copy.
If you change the loop above to:

C#

foreach (string t in Tests)
{
  MatchCollection allMatches = FindDup.Matches(t);
  Trace.WriteLine(string.Format("{0}: {1}", t, allMatches.Count));
  foreach (Match item in allMatches)
  {
    Trace.WriteLine(string.Format(@"  ""{0}"" is doubled", item.Groups[1]));
  }
}

You'll see that.
If the objective is to remove the duplications, then use of Replace() method of the Regex will do the job:

C#

string t2 = FindDup.Replace(t, string.Empty);
Trace.WriteLine(string.Format(@"Final: ""{0}""", t2));

Of course, a different string can be substituted in instead of string.Empty