Extracting the first 10 lines of a file to a strin

问题:

public void get10FirstLines()
{ 
     StreamReader sr = new StreamReader(path);
     String lines = "";
     lines = sr.readLine();
}

How can I get the first 10 lines of the file in the string?

回答1:

Rather than using StreamReader directly, use File.ReadLines which returns an IEnumerable<string>. You can then use LINQ:

var first10Lines = File.ReadLines(path).Take(10).ToList();

The benefit of using File.ReadLines instead of File.ReadAllLines is that it only reads the lines you're interested in, instead of reading the whole file. On the other hand, it's only available in .NET 4+. It's easy to implement with an iterator block if you want it for .NET 3.5 though.

The call to ToList() is there to force the query to be evaluated (i.e. actually read the data) so that it's read exactly once. Without the ToList call, if you tried to iterate over first10Lines more than once, it would read the file more than once (assuming it works at all; I seem to recall that File.ReadLines isn't implemented terribly cleanly in that respect).

If you want the first 10 lines as a single string (e.g. with "\r\n" separating them) then you can use string.Join:

var first10Lines = string.Join("\r\n", File.ReadLines(path).Take(10));

Obviously you can change the separator by changing the first argument in the call.

回答2:

var lines = File.ReadAllLines(path).Take(10);

回答3:

You may try to use File.ReadLines. Try this:-

var lines = File.ReadLines(path).Take(10);

In your case try this as you want the first 10 lines as a single string so you may try to use string.Join() like this:

var myStr= string.Join("", File.ReadLines(path).Take(10));

回答4:

StringBuilder myString = new StringBuilder();

TextReader sr = new StreamReader(path);

for (int i=0; i < 10; i++)
{
myString.Append(sr.ReadLine())
}

回答5:

String[] lines = new String[10];
for (int i = 0; i < 10; i++)
     lines[i] = sr.readLine();

That loops ten times and places the results in a new array.

回答6:

public void skip10Lines()
{ 
    StringBuilder lines=new StringBuilder();
    using(StreamReader sr = new StreamReader(path))
    {
     String line = "";
     int count=0;

      while((line= sr.ReadLine())!=null)
      {
         if(count==10)
           break;
         lines.Append(line+Environment.NewLine);
         count++;
      }
     }

 string myFileData=lines.ToString();
 }

OR

public void skip10Lines()
{ 
     int count=0;
     List<String> lines=new List<String>();
     foreach(var line in File.ReadLines(path))
     {
         if(count==10)
           break;
         lines.Add(line);
         count++;
     }
 }

回答7:

In Groovy, a JVM based language, one approach is:

def buf = new StringBuilder()

Iterator iter = new File(path).withReader{
    for( int cnt = 0;cnt < 9;cnt++){    
        buf << it.readLine()
    }
}

println buf

Since, there is no 'break' from a closure, the loop is nested within the closure, and thereby the resource handling is taken care of by the Groovy runtime.