CODEWITHSUNDEEP
c#linqdictionary
user2380844
user2380844

Reputation: 307

c# if key exist in dictionary still add the value in dictionary

From a datatable I am fetching the value and putting in a Dictionary<string,string>:

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

my datatable for ex is

Value     RowOrder    
page1       01 
page2       00
page3       00

I am using LINQ to fetch the RowOrder according to value given and putting into mydic:

string id = (from DataRow dr in table3.Rows where (string)dr["Value"] == formula
             select (string)dr["RowOrder"]).FirstOrDefault();
mydic.Add(id,Value);

If I run this, error is showing:

"An item with the same key has already been added."

How to overcome this. I want page1, page2, page3 should be added with values 01, 00, 00 respectively

Upvotes: 5

Views: 16827

Answers (5)

Sergey Berezovskiy
Sergey Berezovskiy

Reputation: 236228

Check if key exists before adding 

if (mydic.ContainsKey(id))
    mydic[id] = Value; // or throw exception        
else
    mydic.Add(id, Value);

BTW if you want to convert your DataTable to Dictionary<string, string> with RowOrder as key, and first (or last) Value as value, you can use LINQ:

var mydic = table3.AsEnumerable()
                  .GroupBy(r => r.Field<string>("RowOrder"))
                  .Select(g => g.First()) // or last to use last value for key
                  .ToDictionary(r => r.Field<string>("RowOrder"),
                                     r.Field<string>("Value"));

Upvotes: 3

Alex Filipovici
Alex Filipovici

Reputation: 32561

You may use a Lookup<string,string>:

List<Tuple<string, string>> tuples = new List<Tuple<string, string>>();
tuples.Add(new Tuple<string, string>("01", "page1"));
tuples.Add(new Tuple<string, string>("00", "page2"));
tuples.Add(new Tuple<string, string>("00", "page3"));
var lookup = tuples.ToLookup(t => t.Item1,t=> t.Item2 );

And you may use it like:

var result = lookup["00"];
foreach (var item in result)
{
    Console.WriteLine(item);
}

Which outputs:

page2
page3

Upvotes: 0

Fabio Marcolini
Fabio Marcolini

Reputation: 2375

Use

mydic[id] = Value;

instead of mydic.Add(); The Add method should be used if you want to ensure only one item with a given key is inserted. Note that this overwrite the previously written value.

If you want to have more items with the same key you should use a 

Dictionary<string, IList<string>>

or some other datastructure I don't know of but I would be very glad to hear about since I used that kind of dictionary more than once

Upvotes: 1

DGibbs
DGibbs

Reputation: 14618

You need to check whether the dictionary already has the key before adding to it:

if(!mydic.ContainsKey(id))
{
    mydic.Add(id, Value);
}

A dictionary cannot contain two items with the same key, if you are expecting duplicate id values you need to consider using a different data structure.

Perhaps a List<Tuple<string, string>>?

Upvotes: 9

Tim Schmelter
Tim Schmelter

Reputation: 460138

You can use GroupBy, here a single line approach using Linq-To-DataSet:

Dictionary<string, string> mydic = table3.AsEnumerable()
    .GroupBy(row => row.Field<string>("Value"))
    .ToDictionary(grp => grp.Key, grp => grp.First().Field<string>("RowOrder"));

Upvotes: 1

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