Read text file and compare if the previous line is equal to the current and ignore

Question

1.00/5 (1 vote)

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Hi ,

I'm trying to compare lines in a text file , but the examples I've seen are a bit complicated someone could give me a simple example of how to do it .

example :

"123" , " 234 "
"123" , " 234 " Compare this line to the top
" 134 " , " 664 "

and in the end only show this:

"123" , " 234 "
" 134 " , " 664 "

Thanks

Code:

using System;
using System.IO;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Text.RegularExpressions;
using System.Collections;

namespace ReadTxt
{
    class Program
    {
        static void Main(string[] args)
        {
            StreamReader read = new StreamReader(@"C:\File.txt");
            String line = read.ReadToEnd();
            
            //Do stuff

                Console.WriteLine(line);
                Console.ReadLine();
            
            }           
        }
 }

Posted 11-Jan-15 10:19am

Laxmax1

Updated 11-Jan-15 10:26am

v3

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Comments

Zoltán Zörgő 11-Jan-15 16:20pm

Does not look complicated at all. What have you tried so far?

Sergey Alexandrovich Kryukov 11-Jan-15 16:25pm

What is complicated? :-) Better please tell us what are you missing. Reading a file? Reading a line? String comparison?
—SA

Laxmax1 11-Jan-15 16:27pm

I'm a novice programmer , and the examples that I find not see very clear.

BillWoodruff 11-Jan-15 17:00pm

Is your goal here to only eliminate duplicates when an identical line follows the previous line ... in other words, you don't care if this occurs:

"123" , " 234 "
" 134 " , " 664 "
"123" , " 234 "

So, in that case you would write out the identical line twice ?

2 solutions

Solution 1

It does not require "ideas". Please see my comment to the answer.
Reading file? Please see http://msdn.microsoft.com/en-us/library/system.io.file.readalllines%28v=vs.110%29.aspx[^] or http://msdn.microsoft.com/en-us/library/system.io.streamreader%28v=vs.110%29.aspx[^].
Line comparison? '=='.
Figuring out what to compare with what? Use this: http://en.wikipedia.org/wiki/Brain[^].

[EDIT]

Now I can see your updated question. First, better use using statement: http://msdn.microsoft.com/en-us/library/yh598w02.aspx[^],
http://msdn.microsoft.com/en-us/library/aa664736%28v=vs.71%29.aspx[^].

More importantly, use my last link before [EDIT]. Why reading to the end? The text read to the end is not one text line. You need to read line one by one.

—SA

Posted 11-Jan-15 10:28am

Sergey Alexandrovich Kryukov

Updated 11-Jan-15 15:18pm

v3

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**Zoltán Zörgő** · Accepted Answer · 2015-01-11T10:30:00

Solution 2

Well. Supposing that you need to compare lines using char by char equality, it can be as simple as this:

C#

var result = File.ReadLines(@"D:\TEMP\x.txt").Distinct();

Still, if you need performance, you need to dig deeper to optimize. I have to admit, this is not optimized for comparing only the two consecutive rows. It is doing overall search.
To take only previous line into account, you can use this one instead:

C#

string prev = null; 
foreach(var curr in File.ReadLines(@"D:\TEMP\x.txt"))
{
	if(curr != prev) Console.WriteLine(curr);
	prev = curr;
}

Posted 11-Jan-15 10:30am

Zoltán Zörgő

Updated 11-Jan-15 10:38am

v3

Comments

Laxmax1 11-Jan-15 16:35pm

Thanks :)

Zoltán Zörgő 11-Jan-15 16:39pm

You are welcome. See update also.

Laxmax1 12-Jan-15 14:22pm

My final solucion is this:

string lastLine = " ";
while (reader.Peek() >= 0 )
{
var lines = reader.ReadLine();

if (lines != lastLine){

writer.WriteLine(lines);
lastLine = lines;
}

Zoltán Zörgő 12-Jan-15 14:23pm

Of course, this will also work. :)

Laxmax1 12-Jan-15 14:25pm

thanks for help me bro! :)

BillWoodruff 11-Jan-15 16:57pm

+5 effective simplicity ... is good :) I was tempted to explore a solution using Linq (Distinct), but decided that would be distracting for this OP.

Zoltán Zörgő 11-Jan-15 17:02pm

Thank you. I haven't realized at first sight that OP wants to compare only with the previous line :)

Sergey Alexandrovich Kryukov 11-Jan-15 21:19pm

Sure, a 5.
The only problem I can see is: it doesn't leave OP a chance to solve anything on his own, as this is the main way to learn :-)
—SA

Member 13475664 11-Dec-17 7:43am

can anyone suggest me how to do this in c++