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C#ToArray转换合并为一行,导致数组元素更改

linq arrays c#

Megrez7 · 技术社区 · 3 月前

我想知道是否可以合并 ToArray 将得到的数组单个元素转换为一个语句。

这工作得很好

var response = Enumerable.Range(1, 5).Select(index => new WeatherForecast
{
    Date = DateOnly.FromDateTime(DateTime.Now.AddDays(index)),
    TemperatureC = Random.Shared.Next(-20, 55),
    Summary = Summaries[Random.Shared.Next(Summaries.Length)]
})
.ToArray();

response[0].Summary = "Some text";

return response;

但是,此函数只返回包含在中的字符串 Summary

return Enumerable.Range(1, 5).Select(index => new WeatherForecast
{
    Date = DateOnly.FromDateTime(DateTime.Now.AddDays(index)),
    TemperatureC = Random.Shared.Next(-20, 55),
    Summary = Summaries[Random.Shared.Next(Summaries.Length)]
})
.ToArray()[0].Summary = "Some text";

2 回复 | 直到 3 月前

Dmitrii Bychenko 3 月前

好吧,要有Linq唯一的解决方案,你可以尝试添加三元运算符:

  Summary = index == 1 
    ? "Some text" 
    : Summaries[Random.Shared.Next(Summaries.Length)]

代码:

return Enumerable
  .Range(1, 5)
  .Select(index => new WeatherForecast {
    Date = DateOnly.FromDateTime(DateTime.Now.AddDays(index)),
    TemperatureC = Random.Shared.Next(-20, 55),
    Summary = index == 1 
      ? "Some text" // 1st item is special one
      : Summaries[Random.Shared.Next(Summaries.Length)] // business as usual
  })
  .ToArray();

另一种(更普遍的)可能性是 Select 最后:

return Enumerable
  .Range(1, 5)
   ...
   /* A lot of Linq here */
   ...
  .Select((value, index) => index == 0 
     ? "Some text"
     : value)
  .ToArray();

Ivan Petrov 3 月前

如果你必须在一行上,你总是可以使用这样的扩展方法:

public static class Extensions {
    public static T[] WithChangeAt<T>(this T[] arr, int index, Action<T> change)
    where T : class {
        if ((uint)index >= (uint)arr.Length)
            throw new ArgumentException("Index is out of bounds for the array");
            
        change(arr[index]);
        return arr;
    }
}

然后

return Enumerable.Range(1, 5).Select(index => new WeatherForecast
{
    Date = DateOnly.FromDateTime(DateTime.Now.AddDays(index)),
    TemperatureC = Random.Shared.Next(-20, 55),
    Summary = Summaries[Random.Shared.Next(Summaries.Length)]
})
.ToArray()
.WithChangeAt(0, x => x.Summary = "Some text");