C#4.0新特性之(四)新的LINQ擴充方法-Zip()
1.簡介
所謂zip(中文有拉鏈的意思),就是像拉鏈一樣,把兩個list縫合在一起。Python中有個zip函數可以用來方便的合并兩個或者多個集合,例如:
>>> firstName=['Freesc','Joshua','Ken']
>>> lastName=['Huang','Guan','Wang']
>>> for f,l in zip(firstName,lastName):
print('{0} {1}'.format(f,l))
以上代碼會列印出
Freesc Huang
Joshua Guan
Ken Wang
在C#4.0中,我們可以看到一個類似的擴充函數[1]:
代碼2
//
// Summary:
// Merges two sequences by using the specified predicate function.
//
// Parameters:
// first:
// The first sequence to merge.
//
// second:
// The second sequence to merge.
//
// resultSelector:
// A function that specifies how to merge the elements from the two sequences.
//
// Type parameters:
// TFirst:
// The type of the elements of the first input sequence.
//
// TSecond:
// The type of the elements of the second input sequence.
//
// TResult:
// The type of the elements of the result sequence.
//
// Returns:
// An System.Collections.Generic.IEnumerable<T> that contains merged elements
// of two input sequences.
public static IEnumerable<TResult> Zip<TFirst, TSecond, TResult>(this IEnumerable<TFirst> first,
IEnumerable<TSecond> second,
Func<TFirst, TSecond, TResult> resultSelector);
它可以用來合并列表,並且提供了自訂的組合規則:Func<TFirst, TSecond, TResult> resultSelector。
2.樣本
下面是一段和代碼1功能一樣的C#4.0程式:
代碼3
List<String> firstName = new List<String> { "Freesc", "Joshua", "Ken" };
List<String> lastName = new List<String> { "Huang", "Guan", "Wang" };
foreach (var name in firstName.Zip(lastName, (fname, lname) => fname + " " + lname))
{
Console.WriteLine(name);
}
3.Zip()的實現
在python中要實現一個zip,很簡單(這裡省去了異常處理),只需要用到三個內建函數,iter,map和next:
def zip(*iterables):
# zip('ABCD', 'xy') --> Ax By
iterables = map(iter, iterables)
while iterables:
yield tuple(map(next, iterables))
類似的,如果不考慮異常處理,C#的Zip擴充方法可以是如下實現[2]:
代碼5
static class Enumerable
{
public static IEnumerable<TResult> Zip<TFirst, TSecond, TResult>(this IEnumerable<TFirst> first,
IEnumerable<TSecond> second,
Func<TFirst, TSecond, TResult> func)
{
var ie1 = first.GetEnumerator();
var ie2 = second.GetEnumerator();
while (ie1.MoveNext() && ie2.MoveNext())
yield return func(ie1.Current, ie2.Current);
}
}
4.總結
Zip作為LINQ系統的新成員,提供了一種自由組合兩個集合的方式,要注意的是,這個Zip使用時要求兩個序列的長度一致,如果不一致,它會yield較短的長度。這一點和python中的zip是一樣的。另外,您不妨可以試著寫一個組合多個集合的MultiZip方法,也許它對您更加有用;-)
5.引用
[1] http://msdn.microsoft.com/en-us/library/dd267698(VS.100).aspx
[2] http://community.bartdesmet.net/blogs/bart/archive/2008/11/03/c-4-0-feature-focus-part-3-intermezzo-linq-s-new-zip-operator.aspx
AUTHOR: Freesc Huang @ CNBlogs