var a = new Collection<string> {"a", "b", "c"};
var b = new Collection<int> { 1, 2, 3 };
What is the most elegant way to iterate through both yielding a set of results "a1", "b2", "c3"?
views:
140answers:
4
+10
A:
This is known as "zipping" or "zip joining" two sequences. Eric Lippert describes this very algorithm and provides an implementation.
Andrew Hare
2009-12-02 01:06:36
Great extension, exactly what I was looking for. BTW, I've added a third method, ZipToTuple and it became var c = a.Zip2Tuple(b);
Sergey Aldoukhov
2009-12-02 04:35:44
+3
A:
The mighty Bart de Smet talks about zip functions here:
His most elegant solution takes advantage of an overload of select that takes a 2 parameter Func delegate as its parameter.
a.Select((t,i)=>new{t,i});
In this example, i simply represents the index of the item being processed. So you can create 2 new enumerables of these anonymous objects and join them on i.
Performance-wise, I'd go with a more obvious yielding loop.
spender
2009-12-02 01:10:10
+2
A:
To supplement the great posts by Eric and Bart, here's an implementation using System.Linq 3.5 operators:
public static IEnumerable<TResult> Zip<TFirst, TSecond, TResult> (
this IEnumerable<TFirst> first,
IEnumerable<TSecond> second,
Func<TFirst, TSecond, TResult> resultSelector)
{
return from aa in a.Select((x, i) => new { x, i })
join bb in b.Select((y, j) => new { y, j })
on aa.i equals bb.j
select resultSelector(aa.x, bb.y);
}
dahlbyk
2009-12-02 01:15:35
The runtime of this is horrible, it is effectively n^2 for what should be a linear operation. Eric's blog entry has a .Net 3.5 implementation of Zip that fits this.
Chris
2009-12-02 01:18:44
Not optimal, but definitely not n^2 - runtime is linear by the approximately a.Count() + b.Count(). Join works by building a lookup table by the key (our index); once the cache is built in linear time, lookups are O(1). If anything, the main objection to this approach is the additional memory cost.
dahlbyk
2009-12-02 01:37:58
Oh geez, you are right. I didn't know it was a doing a hash match, I thought it would result in nested loops. Good to know! Sorry for the confusion.
Chris
2009-12-02 01:54:03
No worries - it would use nested loops in the SelectMany generated by from/from/where.
dahlbyk
2009-12-02 02:03:22
+1
A:
You can create an iterator block to handle this elegantly:
public static class Ext
{
public static IEnumerable<string> ConcatEach(this IEnumerable a,
IEnumerable b)
{
var aItor = a.GetEnumerator();
var bItor = b.GetEnumerator();
while (aItor.MoveNext() && bItor.MoveNext())
yield return aItor.Current.ToString() + bItor.Current;
}
}
Call it elegantly =) as:
var a = new Collection<string> {"a", "b", "c"};
var b = new Collection<int> {1, 2, 3};
foreach(var joined in a.ConcatEach(b))
{
Console.WriteLine(joined);
}
gWiz
2009-12-02 01:30:31