Replace found line in text document

Question

I got this code, which finds doubles with odd indexes to replace all with "X" except first one with odd index but keeps all doubles with even indexes. Question is how to replace found line in text document. This way I got result which must be replaced but how to overwrite lines in text document

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.IO;

namespace ConsoleApplication1
{
    class Program
    {
        const string FILENAME = "test.txt";
        static void Main(string[] args)
        {
            List<string> uniqueOddLines = new List<string>();
            List<string> lines = new List<string>();
            string inputLine = "X";
            StreamReader reader = new StreamReader(FILENAME);
            int index = 0;
            while ((inputLine = reader.ReadLine()) != null)
            {
                inputLine = inputLine.Trim();
                if (++index % 2 == 0)
                {
                    lines.Add(inputLine);
                }
                else
                {
                    if (uniqueOddLines.Contains(inputLine))
                    {
                        lines.Add(string.Format("Rewrite line {0}", index));
                    }
                    else
                    {
                        uniqueOddLines.Add(inputLine);
                        lines.Add(inputLine);
                    }
                }    
            }   
            foreach (string line in lines)
            {
                Console.WriteLine(line);
            }
            Console.ReadLine();
        }
    }
}

For example content in text document is:

row1
row2
row3 
row4
row5
row6
row3 
row8
row9
row3 
row11 
row3 
row3 
row3

work of given code:

01. row1
02. row2
03. row3 <- keep row with odd index because it is first in order  
04. row4
05. row5
06. row6
07. row3 <- rewrite this double because it is not the first one with odd index
08. row8
09. row9
10. row3 <- keep this double, because row index is even number 
11. row11 
12. row3 <- keep this double, because row index is even number 
13. row3 <- rewrite this double because it is not the first one with odd index
14. row3 <- keep this double, because row index is even number

And here is desired result, same as above, but I want it in text document:

row1
row2
row3 
row4
row5
row6
X
row8
row9
row3 
row11 
row3 
X
row3

Could you, please, provide an example of initial data and expected output? — Dmitry Bychenko, Sep 05 '16 at 13:12
You cant overwrite particular lines in a text document, you have to overwrite the whole document. Luckily you already have the desired content in the `lines`. Just write it to a file with the same name. — enkryptor, Sep 05 '16 at 13:14
related: http://stackoverflow.com/questions/1245243/delete-specific-line-from-a-text-file — slawekwin, Sep 05 '16 at 13:48
same homework, same code https://stackoverflow.com/questions/39323412/how-to-rewrite-doubles-only-for-odd-index-except-uppermost-row-with-odd-and-keep/39323852#39323852 — Slai, Sep 05 '16 at 13:52

Dmitry Bychenko · Accepted Answer · 2016-09-05T14:24:17.460

0

I suggest using Linq: ReadLines will return the file lines and Select is convenient to implement the logic within:

const string FILENAME = "test.txt";

// Side effect (adding into the set while selecting) is very convenient in the context,
// but should be implemented with care 
HashSet<String> appeared = new HashSet<String>();

var result = File
  .ReadLines(FILENAME)
   // index % 2 == 0 since index is zero-based
  .Select((line, index) => !appeared.Add(line.Trim()) && (index % 2 == 0) 
     ? "X"
     : line)
  .ToList(); // materialization, in case you want both Console and File 

foreach (var line in result)
  Console.WriteLine(line);

Console.ReadLine();

In case you want to write the lines back to file as well as onto console:

File.WriteAllLines(FILENAME, result);

edited Sep 05 '16 at 14:24

answered Sep 05 '16 at 13:43

Dmitry Bychenko

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.hello, this way I got different result `row1 row2 row3 row4 row5 row6 row3 row8 row9 X row11 X row3 X` and in document I got this: `line1 X line3 X line5 X line3 X line9 X line11 X line3 X` – Sep 05 '16 at 13:58
@zrubi: sorry, it should be `(index % 2 == 0)`, see my edit – Dmitry Bychenko Sep 05 '16 at 14:04
not sure what I'm doing wrong, I got absolutely correct result with your code on console, but in the text document, no matter write to new file of into the same (I need same) I got this result again `X row2 X row4 X row6 X row8 X row3 X row3 X row3` – Sep 05 '16 at 14:16
@zrub: it seems that you want the output both on console and file; in that case materialize *before* any output (move `ToList` to be after select); see my edit – Dmitry Bychenko Sep 05 '16 at 14:25
exactly, that's what I want, big support – Sep 05 '16 at 14:39

Replace found line in text document

1 Answers1