[英]How to select array index after Where clause using Linq?
Suppose I have the array string[] weekDays = { "Monday", "Tuesday", "Wednesday", "Thursday", "Friday" };
假设我有数组
string[] weekDays = { "Monday", "Tuesday", "Wednesday", "Thursday", "Friday" };
, and I want to find out the index of array elements containing 's'. ,我想找出包含's'的数组元素的索引。 How can I do this using Linq ?
我怎么能用Linq做到这一点?
I've tried int[] indexOfDaysContainingS = weekDays.Where(day => day.Contains("s")).Select((day, index) => index).ToArray();
我试过
int[] indexOfDaysContainingS = weekDays.Where(day => day.Contains("s")).Select((day, index) => index).ToArray();
, but this returns 0,1,2
as presumably it's getting the index of the filtered IEnumberable<string>
after the Where() clause instead. ,但这会返回
0,1,2
因为它可能是在Where()子句之后得到过滤后的IEnumberable<string>
的索引。 If I put the Select() first, then all I have is the index and can't filter by the days. 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。
What do I need to change to make it work and return 1,2,3
instead ? 我需要改变什么来使其工作并返回
1,2,3
?
You could do it this way: 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();
Not sure if this is optimal.. 不确定这是否是最佳的..
Patko's answer is the way to go in the general case. 帕特科的回答是一般情况下的方法。
Here are 2 more options: 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();
// 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();
这应该工作:
weekDays.Where(a => a.Contains("s")).Select((a, i) => i).ToArray();
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