Using more than one object to iterate though in foreach loops

Question

I have a multidimensional list:

    List<string>[] list = new List<string>[2];
    list[0] = new List<string>();
    list[1] = new List<string>();

And I iterate though the list as follows - but this only iterates through one list:

foreach (String str in dbConnectObject.Select()[0])
{
   Console.WriteLine(str);
}

Although I want to be able to do something like:

foreach (String str in dbConnectObject.Select()[0] & String str2 in dbConnectObject.Select()[1])
{
   Console.WriteLine(str + str2);
}

Sergey Kalinichenko · Accepted Answer · 2012-07-08 12:04:02Z

6

If the lists are of the same size, you can use Enumerable.Zip:

foreach (var p in dbConnectObject.Select()[0].Zip(dbConnectObject.Select()[1], (a,b) => new {First = a, Second = b})) {
    Console.Writeline("{0} {1}", p.First, p.Second);
}

answered Jul 8, 2012 at 12:04

Sergey Kalinichenko

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Comments

Steve B · Accepted Answer · 2012-07-08 12:05:14Z

2

If you want to sequentially iterate through the two lists, you can use IEnumerable<T>.Union(IEnumerable<T>) extension method :

IEnumerable<string> union = list[0].Union(list[1]);

foreach(string str int union)
{
     DoSomething(str);
}

If you want a matrix of combination, you can join the lists :

var joined = from str1 in list[0]
             from str2 in list[1]
             select new { str1, str2};


foreach(var combination in joined)
{
    //DoSomethingWith(combination.str1, combination.str2);
    Console.WriteLine(str + str2);
}

answered Jul 8, 2012 at 12:05

Steve B

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1 Comment

Tim Schmelter Over a year ago

Union will exclude duplicates from the return set. I don't think that this is desired. I would prefer Concat although Zip might be more suitable.

Adam · Accepted Answer · 2012-07-08 12:39:48Z

0

You can try the following code. It also works if the sizes differ.

for (int i = 0; i < list[0].Count; i++)
{
    var str0 = list[0][i];
    Console.WriteLine(str0);
    if (list[1].Count > i)
    {
        var str1 = list[1][i];
        Console.WriteLine(str1);
    }
}

edited Jul 8, 2012 at 12:39

answered Jul 8, 2012 at 12:07

Adam

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1 Comment

Tim Schmelter Over a year ago

Why are you using the Enumerable extension methods on pure Lists? (Count() instead of Count, ElementAt instead of the indexer)

FanAs · Accepted Answer · 2012-07-08 12:07:27Z

-1

Use LINQ instead:

foreach (var s in list.SelectMany(l => l)) { Console.WriteLine(s); }

answered Jul 8, 2012 at 12:07

FanAs

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1 Comment

Tim Schmelter Over a year ago

Ths does not join both lists with each other.

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