如何在使用Linq的Where子句后选择数组索引？

Question

假设我有数组string[] weekDays = { "Monday", "Tuesday", "Wednesday", "Thursday", "Friday" };,我想找出包含's'的数组元素的索引.我怎么能用Linq做到这一点？

我已经尝试了int[] indexOfDaysContainingS = weekDays.Where(day => day.Contains("s")).Select((day, index) => index).ToArray();,但这0,1,2可能会返回,因为它可能是IEnumberable<string>在Where()子句之后得到过滤的索引.如果我首先放置Select(),那么我所拥有的只是索引,不能按天来过滤.

我需要改变什么来使其工作并返回1,2,3？

Answer 1

你可以这样做:

weekDays.Select((day, index) => new { Day = day, Index = index })
        .Where(x => x.Day.Contains("s"))
        .Select(x => x.Index)
        .ToArray();

不确定这是否是最佳的..

Answer 2

帕特科的回答是一般情况下的方法.

这里有2个选项:

// Idea only works with collections that can be accessed quickly by index.
int[] indices = Enumerable.Range(0, weekDays.Length)
                          .Where(index => weekDays[index].Contains("s"))
                          .ToArray();

使用MoreLinq:

// Similar to Patko's idea, except using a 'named' type.
int[] indices = weekDays.AsSmartEnumerable()
                        .Where(item => item.Value.Contains("s"))
                        .Select(item => item.Index)
                        .ToArray();