Quickest way to retrieve data from a very large text file?

Question

0.00/5 (No votes)

See more:

Hi,

I am looking for some advice on how to retrieve data from a very large text file. The file has over 1,000,000 lines of data in it. The data on each line is of fixed length (see below):

GEO   26.509 S30 59  0.000 E154 44  0.000     -4.80      0.13
GEO   26.508 S30 59  0.000 E154 45  0.000     -4.63      0.26
GEO   26.505 S30 59  0.000 E154 46  0.000     -4.58      0.52
GEO   26.500 S30 59  0.000 E154 47  0.000     -4.52      0.78
GEO   26.492 S30 59  0.000 E154 48  0.000     -4.52      0.97
GEO   26.484 S30 59  0.000 E154 49  0.000     -4.52      1.04
GEO   26.476 S30 59  0.000 E154 50  0.000     -4.52      1.17

I'm unclear how to approach this problem. I'm looking for the quickest method to retrieve the data. So far I've tried creating a string list to read all the data from the file, then try to read individual lines of data using the ElementAt method. However this appears to be quite slow if using this method numerous times (ie in a loop).

What I have tried:

Int lineNumber = 2435;

String fileName = "c:\big_file.dat";
String line = String.Empty;

IEnumerable<string> lines = File.ReadLines(fileName);

for (int i = 0; 200 < length; i++)
            {
             line = lines.ElementAt(i);
             // do something else here..
            }

Any ideas?

Posted 17-Mar-21 17:17pm

Elfy71

Updated 17-Mar-21 20:15pm

Add a Solution

3 solutions

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

BillWoodruff · Answer 1 · 2021-03-17T18:53:00

Quote:
However this appears to be quite slow if using this method numerous times (ie in a loop).

As long as you need to process each line, you will have this overhead; is there any way to optimize your line processing function ?

to avoid excess memory use: use a StreamReader to read the file one line at a time: then process the line

using (StreamReader sr = new StreamReader(YourFilePath))
{
    string line;
    
    while (! sr.EndOfStream)
    {
        // your code to process the line
        // YourDoSomething(line);
    }
}

Gerry Schmitz · Answer 2 · 2021-03-17T20:07:00

Solution 2

Use a StringReader.

StringReader Class (System.IO) | Microsoft Docs[^]

For even higher performance, you can use a BinaryReader.

BinaryReader Class (System.IO) | Microsoft Docs[^]

Posted 17-Mar-21 20:07pm

Gerry Schmitz

Comments

Maciej Los 18-Mar-21 3:17am

5ed!

Patrice T · Answer 3 · 2021-03-17T20:15:00

Quote:
Quickest way to retrieve data from a very large text file?

The answer is : depends on what you mean by 'retrieve data'.
- Do you need to process all lines ?
- Do you know lines numbers of lines you want to process ?
- Do you need to need to process lines 1 by 1 and forget them after ?
- Do you need to find a line by its contain ?
- Is the file grow or change with time ?

The answer to those questions imply a different way to speed up the operation. Loading the whole file in lines is only the easiest for you.

File functions allow you to read line by line, jump to a position.
You can also load the file in a database.

Quickest way to retrieve data from a very large text file?

3 solutions

Solution 1

Solution 2

Solution 3

Add your solution here

Preview 0