如何使用LINQ获得指标？ [英] How to get index using LINQ?

问题描述

由于数据源这样的：

var c = new Car[]
{
  new Car{ Color="Blue", Price=28000},
  new Car{ Color="Red", Price=54000},
  new Car{ Color="Pink", Price=9999},
  // ..
};

我如何能找到的指数的第一辆车满足一定条件的LINQ？

How can I find the index of the first car satisfying a certain condition with LINQ?

编辑：

我能想到的，这样的事情，但它看起来可怕的：

I could think of something like this but it looks horrible:

int firstItem = someItems.Select((item, index) => new    
{    
    ItemName = item.Color,    
    Position = index    
}).Where(i => i.ItemName == "purple")    
  .First()    
  .Position;

会不会是最好的解决这一与普通的旧循环？

Will it be the best to solve this with a plain old loop?

推荐答案

这是的IEnumerable 不是一个有序集合。
虽然大多数IEnumerables是有序的，有的（如词典或的HashSet ）都没有。

An IEnumerable is not an ordered set.
Although most IEnumerables are ordered, some (such as Dictionary or HashSet) are not.

因此​​，LINQ不具有的IndexOf 方法。

Therefore, LINQ does not have an IndexOf method.

不过，你可以写一个自己：

However, you can write one yourself:

///<summary>Finds the index of the first item matching an expression in an enumerable.</summary>
///<param name="items">The enumerable to search.</param>
///<param name="predicate">The expression to test the items against.</param>
///<returns>The index of the first matching item, or -1 if no items match.</returns>
public static int FindIndex<T>(this IEnumerable<T> items, Func<T, bool> predicate) {
    if (items == null) throw new ArgumentNullException("items");
    if (predicate == null) throw new ArgumentNullException("predicate");

    int retVal = 0;
    foreach (var item in items) {
        if (predicate(item)) return retVal;
        retVal++;
    }
    return -1;
}
///<summary>Finds the index of the first occurence of an item in an enumerable.</summary>
///<param name="items">The enumerable to search.</param>
///<param name="item">The item to find.</param>
///<returns>The index of the first matching item, or -1 if the item was not found.</returns>
public static int IndexOf<T>(this IEnumerable<T> items, T item) { return items.FindIndex(i => EqualityComparer<T>.Default.Equals(item, i)); }

这篇关于如何使用LINQ获得指标？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！