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();
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.
I think you need to concat the result into line_list
for(i=0; i<10; i++)
{
var fieldsList = from line in File.ReadLines(files[i])
let field = line.Split(',')
where field[2] == "Apple" && !field[3].Contains("Banana")
select field;
line_list = line_list.Concat(fieldsList.Take(100).ToList()).ToList();
}
This is a weird use case for linq, but try take()...
For(i=0;i<10;i++)
line_list = (from line in File.ReadLines(files[i]).Take(100)
let field = line.Split(',')
where field[2] == "Apple" && !field[3].Contains("Banana")
select field).ToList();
Take should be on ReadLines as in Tims example. Otherwise it processes all the lines anyway and then Takes 100.