Getting the array key in a foreach loop

Question

Bear in mind I'm very new to C#.

I'm trying to get the key of the current element in a foreach loop. I know how to do this in PHP but I'm clueless with C#. For example:

foreach($array as $key => $value)
{ 
    echo("$value is assigned to key: $key");
}

What I'm trying to do in C#:

int[] values = { 5, 14, 29, 49, 99, 150, 999 };

foreach(int val in values)
{
    if(search <= val && !stop)
    {
         // set key to a variable
    }
}

Can anyone help me out?

Thanks

Answer 1

Alas there is no built-in way to do this. Either use a for loop or create a temp variable that you increment on each pass.

Answer 2

myKey = Array.IndexOf(values, val);

Answer 3

If you want to get at the key (read: index) then you'd have to use a for loop. If you actually want to have a collection that holds keys/values then I'd consider using a HashTable or a Dictionary (if you want to use Generics).

Dictionary<int, string> items = new  Dictionary<int, string>();

foreach (int key in items.Keys)
{
  Console.WriteLine("Key: {0} has value: {1}", key, items[key]);
}

Hope that helps, Tyler

Answer 4

Actually you should use classic for (;;) loop if you want to loop through an array. But the similar functionality that you have achieved with your PHP code can be achieved in C# like this with a Dictionary:

Dictionary<int, int> values = new Dictionary<int, int>();
values[0] = 5;
values[1] = 14;
values[2] = 29;
values[3] = 49;
// whatever...

foreach (int key in values.Keys)
{
    Console.WriteLine("{0} is assigned to key: {1}", values[key], key);
}

Answer 5

Grauenwolf's way is the most straightforward and performant way of doing this with an array:

Either use a for loop or create a temp variable that you increment on each pass.

Which would of course look like this:

int[] values = { 5, 14, 29, 49, 99, 150, 999 };

for (int key = 0; key < values.Length; ++key)
  if (search <= val && !stop)
  {
    // set key to a variable
  }

With .NET 3.5 you can take a more functional approach as well, but it is a little more verbose at the site, and would likely rely on a couple support functions for visiting the elements in an IEnumerable. Overkill if this is all you need it for, but handy if you tend to do a lot of collection processing.

Answer 6

I answered this in another version of this question:

Foreach is for iterating over collections that implement IEnumerable. It does this by calling GetEnumerator on the collection, which will return an Enumerator.

This Enumerator has a method and a property:

* MoveNext()
* Current

Current returns the object that Enumerator is currently on, MoveNext updates Current to the next object.

Obviously, the concept of an index is foreign to the concept of enumeration, and cannot be done.

Because of that, most collections are able to be traversed using an indexer and the for loop construct.

I greatly prefer using a for loop in this situation compared to tracking the index with a local variable.

http://stackoverflow.com/questions/43021/c-get-index-of-current-foreach-iteration#43029

Answer 7

Here's a solution I just came up with for this problem

Original code:

int index=0;
foreach (var item in enumerable)
{
    blah(item, index); // some code that depends on the index
    index++;
}

Updated code

enumerable.ForEach((item, index) => blah(item, index));

Extension Method:

    public static IEnumerable<T> ForEach<T>(this IEnumerable<T> enumerable, Action<T, int> action)
    {
        var unit = new Unit(); // unit is a new type from the reactive framework (http://msdn.microsoft.com/en-us/devlabs/ee794896.aspx) to represent a void, since in C# you can't return a void
        enumerable.Select((item, i) => 
            {
                action(item, i);
                return unit;
            }).ToList();

        return pSource;
    }

Answer 8

You can implement this functionality yourself using an extension method. For example, here is an implementation of an extension method KeyValuePairs which works on lists:

public struct IndexValue<T> {
    public int Index {get; private set;}
    public T Value {get; private set;}
    public IndexValue(int index, T value) : this() {
        this.Index = index;
        this.Value = value;
    }
}

public static class EnumExtension
{
    public static IEnumerable<IndexValue<T>> KeyValuePairs<T>(this IList<T> list) {
        for (int i = 0; i < list.Count; i++)
            yield return new IndexValue<T>(i, list[i]);
    }
}