Is there a C# equivalent of Python's enumerate() and Ruby's each_with_index?
Best Answer
I keep this extension method around for this:
public static void Each<T>(this IEnumerable<T> ie, Action<T, int> action){var i = 0;foreach (var e in ie) action(e, i++);}And use it like so:
var strings = new List<string>();strings.Each((str, n) =>{// hooray});Or to allow for break-like behaviour:
public static bool Each<T>(this IEnumerable<T> ie, Func<T, int, bool> action){int i = 0;foreach (T e in ie) if (!action(e, i++)) return false;return true;}var strings = new List<string>() { "a", "b", "c" };bool iteratedAll = strings.Each ((str, n)) =>{if (str == "b") return false;return true;});In C#, the foreach loop allows you to iterate over a collection of items. By default, it doesn't provide an index value for each iteration. However, there are scenarios where you may need to access the index of the current item. To achieve this, you can use the foreach loop with an int variable to keep track of the index.
To use the foreach loop with an index, you can declare an additional int variable before the loop starts. This variable will act as the index counter. Inside the loop, you can increment this counter variable by one for each iteration.
Here's an example of using the foreach loop with an index in C#:
string[] fruits = { "apple", "banana", "orange" };int index = 0;foreach (string fruit in fruits){Console.WriteLine($"Fruit at index {index}: {fruit}");index++;}In the above example, we have an array of strings named fruits. The index variable is initialized with zero before the loop starts. Inside the loop, we print the current fruit along with its corresponding index by using string interpolation. Finally, we increment the index by one for each iteration.
You can do the following
foreach (var it in someCollection.Select((x, i) => new { Value = x, Index = i }) ){if (it.Index > SomeNumber) // }This will create an anonymous type value for every entry in the collection. It will have two properties
Value: with the original value in the collectionIndex: with the index within the collection
The C# foreach doesn't have a built in index. You'll need to add an integer outside the foreach loop and increment it each time.
int i = -1;foreach (Widget w in widgets){i++;// do something}Alternatively, you could use a standard for loop as follows:
for (int i = 0; i < widgets.Length; i++){w = widgets[i];// do something}I like being able to use foreach, so I made an extension method and a structure:
public struct EnumeratedInstance<T>{public long cnt;public T item;}public static IEnumerable<EnumeratedInstance<T>> Enumerate<T>(this IEnumerable<T> collection){long counter = 0;foreach (var item in collection){yield return new EnumeratedInstance<T>{cnt = counter,item = item};counter++;}}and an example use:
foreach (var ii in new string[] { "a", "b", "c" }.Enumerate()){Console.WriteLine(ii.item + ii.cnt);}One nice thing is that if you are used to the Python syntax, you can still use it:
foreach (var ii in Enumerate(new string[] { "a", "b", "c" }))Aside from the LINQ answers already given, I have a "SmartEnumerable" class which allows you to get the index and the "first/last"-ness. It's a bit ugly in terms of syntax, but you may find it useful.
We can probably improve the type inference using a static method in a nongeneric type, and implicit typing will help too.
My solution involves a simple Pair class I created for general utility, and which is operationally essentially the same as the framework class KeyValuePair. Then I created a couple extension functions for IEnumerable called Ordinate (from the set theory term "ordinal").
These functions will return for each item a Pair object containing the index, and the item itself.
public static IEnumerable<Pair<Int32, X>> Ordinate<X>(this IEnumerable<X> lhs){return lhs.Ordinate(0);}public static IEnumerable<Pair<Int32, X>> Ordinate<X>(this IEnumerable<X> lhs, Int32 initial){Int32 index = initial - 1;return lhs.Select(x => new Pair<Int32, X>(++index, x));}No, there is not.
As other people have shown, there are ways to simulate Ruby's behavior. But it is possible to have a type that implements IEnumerable that does not expose an index.
This is your collection
var values = new[] {6, 2, 8, 45, 9, 3, 0};Make a range of indexes for this collection
var indexes = Enumerable.Range(0, values.Length).ToList();Use the range to iterate with index
indexes.ForEach(i => values[i] += i);indexes.ForEach(i => Console.Write("[{0}] = {1}", i, values[i]));I just figured out interesting solution:
public class DepthAware<T> : IEnumerable<T>{private readonly IEnumerable<T> source;public DepthAware(IEnumerable<T> source){this.source = source;this.Depth = 0;}public int Depth { get; private set; }private IEnumerable<T> GetItems(){foreach (var item in source){yield return item;++this.Depth;}}public IEnumerator<T> GetEnumerator(){return GetItems().GetEnumerator();}IEnumerator IEnumerable.GetEnumerator(){return GetEnumerator();}}// Generic type leverage and extension invokingpublic static class DepthAware{public static DepthAware<T> AsDepthAware<T>(this IEnumerable<T> source){return new DepthAware<T>(source);}public static DepthAware<T> New<T>(IEnumerable<T> source){return new DepthAware<T>(source);}}Usage:
var chars = new[] {'a', 'b', 'c', 'd', 'e', 'f', 'g'}.AsDepthAware();foreach (var item in chars){Console.WriteLine("Char: {0}, depth: {1}", item, chars.Depth);}It depends on the class you are using.
Dictionary<(Of <(TKey, TValue>)>) Class For Example Support This
The Dictionary<(Of <(TKey, TValue>)>) generic class provides a mapping from a set of keys to a set of values.
For purposes of enumeration, each item in the dictionary is treated as a KeyValuePair<(Of <(TKey, TValue>)>) structure representing a value and its key. The order in which the items are returned is undefined.
foreach (KeyValuePair kvp in myDictionary) {...}