有单行LINQ方式可以做到这一点吗？

Question

Imagine an input text file with the format:

blaha|blahb
blahc|blahd

ie a pipe separated file with 2 columns. Right now, I'm loading it like this:

File.ReadAllLines(...).Select(x =>
{
   string[] arr = x.Split(new char[] { '|' });
   return new Item(arr[0], arr[1]);
};

If I change the first line to .Select(x => x.Split(new char[] { '|' }) it's going to return every row and column as an array element which is not what I want. Is there a linq "inline" way to split the columns and new up the object?

Answer 1

You can chain multiple selects together.

File.ReadAllLines(...)
    .Select(line => line.Split(new [] { '|' }))
    .Select(arr => new Item(arr[0], arr[1]))

One thing i do for this type of work as well is to create helper methods that you can use as Method Groups if this type of functionality is going to be reused.

public class Item {
    ...
    public static Item FromPipeDelimitedText(string text) {
        var arr = text.Split(new [] { '|' };
        return new Item(arr[0], arr[1]);
    }
}

then

File.ReadAllLines(...).Select(Item.FromPipeDelimitedText);

with this method the functionality that extracts the data from the file can be tested independently

Answer 2

"Cooler" is about as opinion-based as it gets, but you can't argue that this isn't LINQ, or that it has more than one semicolon.

var items =
    from line in File.ReadAllLines(myfile)
    let arr = line.Split(new char[] { '|' })
    select new Item(arr[0], arr[1]);

Here's a filddle demonstrating the above code . System.IO.File.ReadAllLines(string path) returns string[] -- an array of lines from the file.

Answer 3

You can always do this:

File.ReadAllLines(someFileName)
    .Select(x => x.Split('|'))
    .Select(a => new Item(a[0], a[1]));

This however assumes that the line always splits in [at least] two, which from personal experience is not easily error-handled.

I would suggest avoiding a single-line approach unless you are absolutely sure there will be no problem lines or use a function delegate to manage the instantiation and error handling.

Answer 4

Use SelectMany .

// returns IEnumerable<Item>
File.ReadAllLines(...).SelectMany(x =>
{
   string[] arr = x.Split(new char[] { '|' });
   return new Item(arr[0], arr[1]);
}