成对分组项目 [英] Group items in pairs
问题描述
我有项目列表,例如:{ i1, i2, i3, i4, i5, i6, i7 }
.
我想获取一个列表,其中每个项目都是源列表中的一对项目:{ {i1, i2}, {i3, i4}, {i5, i6}, {i7} }
.
i7
是成对的单个项目,因为没有项目i8
.
可以用LINQ吗?
I have list of items, for example: { i1, i2, i3, i4, i5, i6, i7 }
.
I want to get a list, where every item is a pair of items from source list: { {i1, i2}, {i3, i4}, {i5, i6}, {i7} }
.
i7
is a single item in pair because there is no item i8
.
Is it possible to do with LINQ?
推荐答案
好吧,你可以做:
var pairs = sequence.Select((value, index) => new { value, index } )
.GroupBy(x => x.index / 2, x => x.value)
结果为IGrouping<int, T>
,其键为0、1、2等,每个组的内容为一项或两项.
The result is an IGrouping<int, T>
with a key of 0, 1, 2 etc and the contents of each group being one or two items.
但是,我可能会编写一个自定义扩展方法:
However, I'd possibly write a custom extension method:
public static IEnumerable<Tuple<T, T>> PairUp<T>(this IEnumerable<T> source)
{
using (var iterator = source.GetEnumerator())
{
while (iterator.MoveNext())
{
var first = iterator.Current;
var second = iterator.MoveNext() ? iterator.Current : default(T);
yield return Tuple.Create(first, second);
}
}
}
这将产生一个元组序列-这里的缺点是,如果该序列具有奇数个项目,则最后一个元组将T
的默认值作为第二个"项目.对于仅包含非空值的序列的引用类型,这是可以的,但对于某些序列,则无济于事.
This will yield a sequence of tuples - the downside here is that the final tuple will have the default value for T
as the "second" item if the sequence has an odd number of items. For reference types where the sequence only consists of non-null values, that's okay, but for some sequences it wouldn't help.
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