编写LINQ查询困难

Question

I have written a query to fetch count of lines matching the criteria.

The linq query that i have used is:

int result = File.ReadLines(filePath).Count(line => line.StartsWith(word));

Here, i require the lines matching the criteria not the count. Please help

Answer 1

File.ReadLines(filePath).Where(line => line.StartsWith(word));

Just change it to a Where instead.

http://msdn.microsoft.com/en-us/library/system.linq.enumerable.where.aspx

Filters a sequence of values based on a predicate.

Answer 2

Use Where :

List<string> lines = File.ReadLines(filePath)
                         .Where(line => line.StartsWith(word)).ToList();

You can then do:

int count = lines.Count;

To get the number of lines matching the predicate

Answer 3

var lines = File.ReadLines(filePath).Where(line => line.StartsWith(word));
var total = lines.Count;

Answer 4

IEnumerable<string> linesMatching = File.ReadLines(filePath)
    .Where(line => line.StartsWith(word));

On this way you have the lines and - if you create a collection from it - also the count:

List<string> lines = linesMatching.ToList();
int count = lines.Count;

Note that you cannot reuse the query once it is executed since you're using File.ReadLines which uses a StreamReader under the hood. Once it was used it is disposed. So this will raise an exception since the query was already executed at ToList :

int count = linesMatching.Count();