[英]How to avoid loop by using LINQ for the following code?
foreach (Feature fe in features)
{
if (fileNames.Any(file => file.Contains(fe.FeatureName)))
{
fe.MatchCount = fe.MatchCount == 0 ? 1 : fe.MatchCount;
}
}
You are mutating the object at the end of the loop-variable, so you can't do that (cleanly) in pure LINQ. 你正在改变循环变量末尾的对象,所以你不能在纯 LINQ中这样做(干净利落)。 Just keep the loop;
保持循环; it'll be simpler to understand, but maybe it can be reduced a bit :
理解起来会更简单,但也许可以减少一点 :
var qry = features.Where(fe => fe.MatchCount == 0 &&
fileNames.Any(file => file.Contains(fe.FeatureName));
foreach (Feature fe in qry) { fe.MatchCount == 1; }
features.Where(f => fileNames.Any(file => file.Contains(f.FeatureName)))
.ToList()
.ForEach(x => x.MatchCount = x.MatchCount == 0 ? 1 : x.MatchCount);
Something worth mentioning is that materializing your query to a list, and then iterating over it again with 'ForEach' can be a pretty expensive call if your list is quite large. 值得一提的是,如果您的列表非常大,将查询实现到列表,然后使用'ForEach'再次迭代它可能是一个非常昂贵的调用。 I would recommend adding the following extension method to give a 'ForEach' method to IEnumerable:
我建议添加以下扩展方法,为IEnumerable提供一个'ForEach'方法:
public static void Map<T>(this IEnumerable<T> source, Action<T> func)
{
foreach (T i in source)
func(i);
}
I call mine Map, but you can call it ForEach if you so choose. 我称之为地图,但如果您愿意,可以将其称为ForEach。 This turns Danny's answer into:
这将Danny的答案变为:
features.Where(f => fileNames.Any(file => file.Contains(f.FeatureName)))
.Map(x => x.MatchCount = x.MatchCount == 0 ? 1 : x.MatchCount);
Func<Feature, Feature> updateMatchCount = (fe) =>{
fe.MatchCount = fe.MatchCount == 0 ? 1 : fe.MatchCount;
return fe;
};
var updatedFeatures = from fe in features
where fileNames.Any(file => file.Contains(fe.FeatureName))
select updateMatchCount(fe);
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