Question

我有一个包含1000行的字符串数组，如何使用linq c＃将每行25行分组为一个文本。我可以使用循环，但我需要使用linq的代码。

Answer 1

var blocks = File.ReadLines(filename)
                    .Select((s, i) => new { s, i })
                    .GroupBy(x => x.i / 25)
                    .Select(g => String.Join(" ", g.Select(x => x.s)))
                    .ToList();

您还可以使用Morelinq的批处理方法：https://code.google.com/p/morelinq/source/browse/MoreLinq/Batch.cs

Answer 2

当问题是关于一个简单的linq时，我认为，答案应该是好看的和高效的。所以，我准备了一个测试用例。

由于这是社区维基，请随时更新..

var arr = Enumerable.Range(0, 20000).Select(x => x.ToString()).ToArray();

var t1 = Measure(() =>
{
    var blocks = arr
                .Select((s, i) => new { s, i })
                .GroupBy(x => x.i / 25)
                .Select(g => String.Join(" ", g.Select(x => x.s)))
                .ToList();
}, 1000);


var t2 = Measure(() =>
{
    var allLines = new List<string>();
    for (int i = 0; i < arr.Length; i += 25)
    {
        allLines.Add(String.Join(" ", arr.Skip(i).Take(25)));
    }

}, 1000);


var t3 = Measure(() =>
{
    int count = 0;
    var blocks = arr
                .GroupBy(x => count++ / 25)
                .Select(g => String.Join(" ", g))
                .ToList();
}, 1000);


var t4 = Measure(() =>
{
    var blocks = arr.Batch(25, x => x)
                .Select(g => String.Join(" ", g))
                .ToList();
}, 1000);


Console.WriteLine("EZI: {0}\nShar1er80: {1}\nModified-EZI: {2}\nMoreLinq'sBatch: {3}", t1,t2,t3,t4);

long Measure(Action action, int n)
{
    action();
    var sw = Stopwatch.StartNew();
    for (int i = 0; i < n; i++)
    {
        action();
    }
    return sw.ElapsedMilliseconds;
}

<强>输出：

EZI: 3548
Shar1er80: 24362
Modified-EZI: 1782
MoreLinq'sBatch: 1300

Answer 3

因为您在问题中标记了take，所以您可以使用Take()中的Linq获得与@EZI相同的结果。

using System;
using System.Collections.Generic;
using System.Linq;

public class Program
{
    public static void Main()
    {
        List<string> _1000Lines = new List<string>();
        for (int i = 1; i <= 1000; i++)
            _1000Lines.Add(i.ToString());

        for (int i = 0; i < _1000Lines.Count; i += 25) 
        {
            // Use Skip() to skip the previous 25 items from the previous iteration
            Console.WriteLine(String.Join(" ", _1000Lines.Skip(i).Take(25)));
        }
    }
}

Fiddle Demo

使用linq

3 个答案: