Question

Im reading csv files into a list. since each file contains many lines and time-consuming to read, I only need to check the first 100 lines for each file. How can I have Linq to only read first 100 lines and then continue to the next file?

For(i=0;i<10;i++)
     line_list = (from line in File.ReadLines(files[i])
                  let field = line.Split(',')
                  where field[2] == "Apple" && !field[3].Contains("Banana")
                  select field).ToList();

Answer 1

You can use Enumerable.Take to take only the first 100 lines:

var first100Lines = File.ReadLines(path).Take(100);

for what it’s worth, here the all in one:

List<List<string[]>> allFileLineColumns = files
    .Select(fPath => 
        File.ReadLines(fPath)
            .Take(100)
            .Select(l => new { Line=l, Cols=l.Split(',') })
            .Where(x => x.Cols.Length >= 4 && x.Cols[2] == "Apple" && !x.Cols[3].Contains("Banana"))
            .Select(x => x.Cols)
            .ToList()
    ).ToList();

Although i would split it into multiple parts to increase readability.