c# Dictionary<string,string> how to loop through items without knowing key [duplicate]

Question

I have a:

var selectedDates = new Dictionary<string, string>();
selectedDates.Add("2014-06-21", DateTime.Now.ToLongDateString());
selectedDates.Add("2014-07-21", DateTime.Now.AddDays(5).ToLongDateString());
selectedDates.Add("2014-08-21", DateTime.Now.AddDays(9).ToLongDateString());
selectedDates.Add("2014-09-21", DateTime.Now.AddDays(14).ToLongDateString());

How can I loop trough items without knowing the key?

For example I want to get the value of the item[0]

If I do:

var item = selectedDates[0].value; // I get an error

Bigg

What do you expect the first item to be? – Inaccessible

why use a dictionary then? Would an array or list not do the job? – Fane

Could you explain if you don't know how to loop over a dictionary or if you have problem to refer to a specific entry in the Dictionary without knowing the key value? – Mestee

Answer 1

How can I loop trough items without knowing the key?

For example I want to get the value of the item[0]

You want to treat the dictionary as (ordered) collection similar to a list or array and get the first item in it?

You can because a Dictionary<string, string> is an IEnumerable<KeyValuePair<string, string>> implicitly. Just use First or FirstOrDefault:

string valueAtFirstPosition = selectedDates.First().Value; 

However, note that a dictionary is not meant to be used as as an ordered collection. It is a collection which can be used to fast-lookup a value by a key. But you can enumerate it anyway.

foreach(KeyValuePair<string, string>keyVal in selectedDates)
{
    Console.WriteLine("Key: {0} Value: {1}", keyVal.Key, keyVal.Value);
}

You should simply not rely on that order. I think in the current implementation the order is stable as long as you don't delete items. Read

Read: Why is a Dictionary “not ordered”?

Asseveration

who upvotes this? "how to loop through items" and you say "use first"? this answer is wrong – Enyo

@AndreasMüller: i understood "item[0]" as "give me the first item" and "loop trough items" as "use it as collection". – Asseveration

@TimeSchmelter question asks for something else. using [0] is OP's way of expressing that he doesn't know how to use a dictionary, and is refusing to read msdn api – Enyo

@AndreasMüller: how do you know? OP is trying to find 0(int) as key even if he adds DateTimes (as string)? Isn't that more unlikely as that he wants the first? – Asseveration

he is adding string keys and expects the indexer to work with an integer. No. If you're using a dictionary that's not what you would want. If he would want the first item he HOPEFULLY would be using a list instead – Enyo

@AndreasMüller: He doesnt expect it to work, he just wants to use it like a list if he wants to access the first. That's why i've mentioned that a dictionary is not meant to be used as as an ordered collection. However, the order is stable as long as you don't modify the dictionary later (to be exact: delete items). – Asseveration

fair enough. In this case you probably guessed his intentions correct and he just doesn't know what collection to use. – Enyo

Answer 2

try this

  foreach (string key in selectedDates.Keys)
  {
        var item = selectedDates[key]; 
  }

Shelving

though this is an amuzing way to do it, wouldn't a foreach(var v in sselectedDates){ var date = v.Value;} be better? – Impartial

Answer 3

It's simple, loop trough it with a foreach or to get a specific index do:

var date = selectedDates.ElementAt(0).Value;

Impartial

Answer 4

Let me put together two things for you. Firstly, you can loop or use LINQ to access elements, just as you could do it in a list as well:

var dict = new Dictionary<string, string>();

// loop
foreach (var item in dict)
{
    var key = item.Key;
    var value = item.Value;
}

// "first" (see below)
var firstItem = dict.First();

However, be aware that what you're referring to as the first item can be pretty much any item in the Dictionary. Dictionaries store elements in any order that is convenient for a lookup (so do sets).

This order is known for some implementations, but lists or arrays might fit better when the order of the elements is important. A Dictionary in .NET is an implementation of a hash table data structure (tree map is another map implementation).

Antediluvian

Answer 5

try this :

foreach(var key in selectedDates.Keys)
{
    var value = selectedDates[key];
}

Stylographic

As Vincent already commented at nsgocev's answer: "wouldn't a foreach(var v in sselectedDates){ var date = v.Value;} be better?" – Zara

Answer 6

Use this overload of Where:

var result = selectedDates.Where((d,i)=>i==0);

Amidase

Answer 7

Try:

foreach (var date in selectedDates)                
{                  
    var item = date.Value;              
}

Martell