how can I read 200 row from a txt file by loop in C#?

diamond diamond

12y1.5kVisual Basic .NET

I have a problem to read a txt file with 200 row. Of course I want to read next step from 2 to 201 like a below.

step 1 : 1th - 200th row of file

step 2: 2th to 201th row of file

step 3: 3th to 202 row

, ....

please help me

Thanks

7 Replies

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Vulpes12y ago
Accepted answer
Well, rather than repeatedly reading the rows from disk, it would be more efficient to read them all into memory in one operation, convert them to doubles and then iterate through successive chunks of 200 doubles:

string[] lines = File.ReadAllLines(filePPath);
double[] values = new double[lines.Length];
double d = 0;

for(int i = 0; i < lines.Length; i++)
{
// note: uses zero if the row can't be parsed to a double
double.TryParse(lines[i], out d);
values[i] = d;
}

for(int i = 0; i <= values.Length - 200; i++)
{
for(int j = 0; j < 200; j++)
{
// do something with values[i + j]
}
}
diamond diamond12y ago
Thanks so much Vulpes
Vulpes12y ago
values.Length - 200 is the last value of 'i' for which there will still be 200 elements remaining in the values array.

Those elements will have indices from values.Length - 200 to values.Length - 1, inclusive. The latter is of course the last element of the array.
diamond diamond12y ago
Thanks so much Vulpes, Just let me know why use value.lemght-200 in loop? I need the value of text file for computing an etnropy, so I need each time, select values of first row to value of 200th row and next time values of second row to 201 rows, so on.
diamond diamond12y ago
I should say my txt file contains double type. I want to read the these values by first row to 200 row the next step read the values from second to 201th row. and ...
diamond diamond12y ago
Hi Vulpes,

Thanks your help. I have more than 1000 row, I want to select 200 row of the file but with some condition that I mentioned it such as below:

I donot know it can be by loop or linq or ...?

step 1 : 1th - 200th row of file

step 2: 2th to 201th row of file

step 3: 3th to 202 row
, ....
Vulpes12y ago
Your question doesn't make much sense because, if there are 200 rows in the file, how can there be a 201st and 202nd row?

However, to read however may rows there are in a loop, you can do this:

using System.IO;
//....

using(StreamReader sr = new StreamReader(filePath))
{
string line;
while((line = sr.ReadLine()) != null)
{
// do something with 'line'
}
}