C #4.0 new features (4) New LINQ Extension Method-zip ()

C #4.0 new features (4) New LINQ Extension Method-zip ()

1. Introduction

The so-called zip (Chinese indicates a zipper) is to stitch two lists together like a zipper. There is a zip function in Python that can be used to conveniently merge two or more sets, for example:

>>> Firstname = ['freesc ', 'jobua', 'ken']
>>> Lastname = ['huang ', 'guany', 'wang']
>>> For F, L in zip (firstname, lastname ):
Print ('{0} {1}'. Format (F, L ))

The above code is printed

Freesc Huang
Joshua Guan
Ken Wang

In C #4.0, we can see a similar extension function [1]:

Code 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 );

It can be used to merge lists and provides custom combination rules: func <tfirst, tsecond, tresult> resultselector.

2. Example

The following is a C #4.0 program with the same function as code 1:

Code 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. Implementation of zip ()

To implement a zip file in Python, it is very simple (Exception Processing is omitted here). You only need to use three built-in functions, ITER, map, and next:

Def zip (* iterables ):
# Zip ('abcd', 'xy') --> ax
Iterables = map (ITER, iterables)
While iterables:
Yield tuple (MAP (next, iterables ))

 

Similarly, if you do not consider exception handling, the C # zip extension method can be implemented as follows [2]:

Code 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. Summary

As a new member of the LINQ system, zip provides a way to freely combine two sets. Note that the length of the two sequences must be consistent during the use of zip. If they are different, it has a short length of yield. This is the same as zip in Python. In addition, you may try to write a multizip method that combines multiple sets, which may be more useful to you ;-)

5. Reference

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