我不知道Linq解决方案——但你可以使用生成器(yield 率-回报率)轻松地自己编写算法.
public static IEnumerable<T> TakeAllButLast<T>(this IEnumerable<T> source) {
var it = source.GetEnumerator();
bool hasRemainingItems = false;
bool isFirst = true;
T item = default(T);
do {
hasRemainingItems = it.MoveNext();
if (hasRemainingItems) {
if (!isFirst) yield return item;
item = it.Current;
isFirst = false;
}
} while (hasRemainingItems);
}
static void Main(string[] args) {
var Seq = Enumerable.Range(1, 10);
Console.WriteLine(string.Join(", ", Seq.Select(x => x.ToString()).ToArray()));
Console.WriteLine(string.Join(", ", Seq.TakeAllButLast().Select(x => x.ToString()).ToArray()));
}
或者作为丢弃最后n项的通用解决方案(使用注释中建议的队列):
public static IEnumerable<T> SkipLastN<T>(this IEnumerable<T> source, int n) {
var it = source.GetEnumerator();
bool hasRemainingItems = false;
var cache = new Queue<T>(n + 1);
do {
if (hasRemainingItems = it.MoveNext()) {
cache.Enqueue(it.Current);
if (cache.Count > n)
yield return cache.Dequeue();
}
} while (hasRemainingItems);
}
static void Main(string[] args) {
var Seq = Enumerable.Range(1, 4);
Console.WriteLine(string.Join(", ", Seq.Select(x => x.ToString()).ToArray()));
Console.WriteLine(string.Join(", ", Seq.SkipLastN(3).Select(x => x.ToString()).ToArray()));
}