Getting the array key in a 'foreach' loop

Question

How do I get the key of the current element in a foreach loop in C#?

For example:

PHP

foreach ($array as $key => $value)
{
             


        

Answer 1

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]);
    }
}

Answer 2

With DictionaryEntry and KeyValuePair:

Based on
MSDN

IDictionary<string,string> openWith = new Dictionary<string,string>()
{
   { "txt", "notepad.exe" }
   { "bmp", "paint.exe" }
   { "rtf", "wordpad.exe" }
};

foreach (DictionaryEntry de in openWith)
{
    Console.WriteLine("Key = {0}, Value = {1}", de.Key, de.Value);
}

// also

foreach (KeyValuePair<string,string> de in openWith)
{
    Console.WriteLine("Key = {0}, Value = {1}", de.Key, de.Value);
}

Releated SO question: KeyValuePair VS DictionaryEntry

Answer 3

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 4

myKey = Array.IndexOf(values, val);

Answer 5

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 6

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);
}