Get first element from a dictionary

Question

I have the following declaration:

Dictionary<string, Dictionary<string, string>> like = new Dictionary<string, Dictionary<string, string>>();

I need to get the first element out, but do not know the key or value. What's the best way to do this?

Answer 1

Note that to call First here is actually to call a Linq extension of IEnumerable, which is implemented by Dictionary<TKey,TValue>. But for a Dictionary, "first" doesn't have a defined meaning. According to this answer, the last item added ends up being the "First" (in other words, it behaves like a Stack), but that is implementation specific, it's not the guaranteed behavior. In other words, to assume you're going to get any defined item by calling First would be to beg for trouble -- using it should be treated as akin to getting a random item from the Dictionary, as noted by Bobson below. However, sometimes this is useful, as you just need any item from the Dictionary.

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Just use the Linq First():

var first = like.First();
string key = first.Key;
Dictionary<string,string> val = first.Value;

Note that using First on a dictionary gives you a KeyValuePair, in this case KeyValuePair<string, Dictionary<string,string>>.

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Note also that you could derive a specific meaning from the use of First by combining it with the Linq OrderBy:

var first = like.OrderBy(kvp => kvp.Key).First();

Answer 2

For anyone coming to this that wants a linq-less way to get an element from a dictionary

var d = new Dictionary<string, string>();
d.Add("a", "b");
var e = d.GetEnumerator();
e.MoveNext();
var anElement = e.Current;
// anElement/e.Current is a KeyValuePair<string,string>
// where Key = "a", Value = "b"

I'm not sure if this is implementation specific, but if your Dictionary doesn't have any elements, Current will contain a KeyValuePair<string, string> where both the key and value are null.

(I looked at the logic behind linq's First method to come up with this, and tested it via LinqPad 4)

Answer 3

Though you can use First(), Dictionaries do not have order per se. Please use OrderedDictionary instead. And then you can do FirstOrDefault. This way it will be meaningful.

Answer 4

EDIT: Use an OrderedDictionary.

It's better to use FirstOrDefault() to retrieve the first value.

Ex:

var firstElement = like.FirstOrDefault();
string firstElementKey = firstElement.Key;
Dictinary<string,string> firstElementValue = firstElement.Value;

Answer 5

using System.Linq;

Dictionary<string, Dictionary<string, string>> like = new Dictionary<string, Dictionary<string, string>>();
Dictionary<string, string> first = like.Values.First();

Answer 6

Dictionary does not define order of items. If you just need an item use Keys or Values properties of dictionary to pick one.

Answer 7

ill find easy way to find first element in Dictionary :)

 Dictionary<string, Dictionary<string, string>> like = 
 newDictionary<string,Dictionary<string, string>>();

 foreach(KeyValuePair<string, Dictionary<string, string>> _element in like)
 {
   Console.WriteLine(_element.Key); // or do something
   break;
 }

Answer 8

convert to Array

var array = like.ToArray();
var first = array[0];

Answer 9

Easy way of to index a Collection in terms of performance, high compatibility (2.0, 3.0, 3.5, 4.0, 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8) and easy implemention.

Save today!! Its not only a items copy, this is items reference of a Collection!! buy it!!

string [] arrayString = new string[like.Count];
like.Values.CopyTo( arrayString,0 );

arrayString[0] //First

References:

https://learn.microsoft.com/es-es/dotnet/api/system.collections.generic.icollection-1.copyto?view=net-5.0

https://social.msdn.microsoft.com/Forums/vstudio/en-US/dc5e4242-64d3-45ac-bdea-cf4f3d9abdbb/icollectioncopyto-vs-arraylisttoarray?forum=netfxbcl