<div>
The best way is to split it based on the delimiter . . .eg the ;. 
 

<pre><code class="code-10 nolinks" id="code-20-41357007-1">string line;
int NodeNumber;

// Read the file and display it line by line.
System.IO.StreamReader file = 
 new System.IO.StreamReader(&quot;c:\\myFile.txt&quot;);
while((line = file.ReadLine()) != null)
{
NodeNumber = -1;
string firstPart = line.Split(new char[]{';'})[0];
 if (int.TryParse(firstPart, out NodeNumber))
 {
 // will only happen if firstPart is parsed
 if (Lnodes.Contains(NodeNumber))
 {
 //Lnodes has this number, do something.
 } 
 }
} 
</code></pre>
</div>

<div>
Hello Kyle, 
it seems not to be exactly what I'm looking for: i need to read first the List and see if its IdNumber value has an equivalent in the .txt files. 
In the solution you wrote, if a NodeNumber does not match with the text file I can't know it 
regards
</div>

<div>
Hi Paulagier; 
 
Try this out, it should give you what you need.
<pre><code class="code-10 nolinks" id="code-20-41357036-1">// File location on disk
string filename = @&quot;C:\Working Directory\data.txt&quot;;
// You list of Lnodes
List&lt;int&gt; Lnodes = new List&lt;int&gt;() { 317, 311, 312, 313, 314, 315, 316, 310 };
// Read the text file into memory
List&lt;string&gt; txtFile = File.ReadAllLines(filename).ToList();
// All the position data is in this List in the same order as Lnodes
List&lt;string&gt; position;

position = (from id in Lnodes
 join pos in txtFile on id.ToString() equals pos.Substring(0, 3)
 select pos.Substring(4)).ToList();
</code></pre>
</div>

<div>
can you write the full example of what your'e trying to do . . . you can know it by adding an else but your requirements aren't clear to me. 
 
&nbsp; if (Lnodes.Contains(NodeNumber)) 
&nbsp; &nbsp;{ 
&nbsp; &nbsp; //Lnodes has this number, do something. 
&nbsp; &nbsp; } 
&nbsp; else 
&nbsp; &nbsp;{ 
&nbsp; &nbsp;//Not in LNOdes . . . do something else? 
&nbsp; }
</div>

<div>
if (Lnodes.Contains(NodeNumber)) 
&nbsp; &nbsp;{ 
&nbsp; &nbsp; //Lnodes has this number, do something. 
&nbsp; &nbsp; } 
&nbsp; else 
&nbsp; &nbsp;{ 
&nbsp; &nbsp;//Not in LNOdes . . . do something else? 
&nbsp; } 
 
The problem comes if an IdNumber value is contained in LNodes and NOT in the .txt file. It seems to me that in your solution i cannot handle that situation. 
Let's add in my example the LNodes value &quot;321&quot; , everything else equal.
</div>

<div>
What do you need to happen when a Lnodes value is NOT in the text file? 
 
Did you try my solution?
</div>

<div>
Dear Fernando 
I nned to store somewhere (list, .txt file..) &nbsp;the IdNumber that is not in the text file
</div>

<div>
So are you saying that you only need the Lnodes numbers &nbsp;that are not in the text file and not a list of a position that are in the file? 
 
If that is not the case, given the two input info, List of Lnodes and the text file, please show with values what you want the resulting object should look like.
</div>

<div>
where are you storing them? 
 
if (!Lnodes.Contains(NodeNumber)) 
&nbsp; &nbsp;{ 
&nbsp; 
&nbsp; &nbsp; //store the NodeNumber 
&nbsp; }
</div>

<div>
List Lnodes &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;.txt file 
310 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 310;UpSpine 
311 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 311;LeftArm 
312 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;312;LeftForeArm 
313 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;313;LeftHand 
314 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;314;MidSpine 
320 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;315;RightForeArm 
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;316;RightArm 
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;317;Pelvis 
 
I need the three subsets: 
In LNodes and in .txt file: &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 310,311,312,313,314 
In LNodes and NOT in .txt file: &nbsp; &nbsp; &nbsp; &nbsp;320 
In .txt file and NOT in vNode: &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;315,316,317
</div>

<div>
A GREAT solution, &nbsp;with a LOT of expertise-behind 
Thanks Fernando
</div>

<div>
<div class="content wysiwyg-content">
Hello experts 
C# 
I have a List Lnodes with just one item per line: an int value &nbsp;named &quot;IdNumber&quot; 
 
I have a .txt file with two items per line: 
- &quot;IdNumber&quot; (always the same lenght and position) 
- a separator (;) 
- &quot;Position&quot; (a string item with different length) 
 
I need to read, line by line, the List Lnodes and, &nbsp;for each value of IdNumber; 
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;- browse the .txt file 
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;- find the line that contains the same IdNumber value 
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;- extract on that line the corresponding &quot;Position&quot; string 
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;- Add that value to a row on another list 
 
I'v tried a lot of methods (substrings, arrays, and so on) and now I'm lost !! 
Hereunder are a sample of Lnodes and another of the .text file 
 
 
List Lnodes 
 
310 
311 
312 
313 
314 
.... 
 
 
 
.txt file 
310;UpSpine 
311;LeftArm 
312;LeftForeArm 
313;LeftHand 
314;MidSpine 
315;RightForeArm 
316;RightArm 
317;Pelvis
</div>
</div>

Hello experts
C#
I have a List Lnodes with just one item per line: an int value  named "IdNumber"

I have a .txt file with two items per line:
- "IdNumber" (always the same lenght and position)
- a separator (;)
- "Position" (a string item with different length)

I need to read, line by line, the List Lnodes and,  for each value of IdNumber;
             - browse the .txt file
             - find the line that contains the same IdNumber value
             - extract on that line the corresponding "Position" string
             - Add that value to a row on another list 

I'v tried a lot of methods (substrings, arrays, and so on) and now I'm lost !!
Hereunder are a sample of Lnodes and another of the .text file


List Lnodes

310
311
312
313
314
....



.txt file
310;UpSpine
311;LeftArm
312;LeftForeArm
313;LeftHand
314;MidSpine
315;RightForeArm
316;RightArm
317;Pelvis

C#  Matching an item in a list with the corresponding item in a text file

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