Select a Dictionary T1 T2 with LINQ

Question

I have used the  select  keyword and extension method to return an IEnumerable lt T gt  with LINQ  but I have a need to return a generic Dictionary lt T1  T2 gt  and can t figure it out   The example I learned this from used something in a form similar to the following    IEnumerable lt T gt  coll   from x in y      select new SomeClass  prop1   value1  prop2   value2      I ve also done the same thing with extension methods   I assumed that since the items in a  Dictionary lt T1  T2 gt  can be iterated as KeyValuePair lt T1  T2 gt  that I could just replace  SomeClass  in the above example with  new KeyValuePair lt T1  T2 gt          but that didn t work  Key and Value were marked as readonly  so I could not compile this code    Is this possible  or do I need to do this in multiple steps   Thanks

User · Accepted Answer

The extensions methods also provide a ToDictionary extension. It is fairly simple to use, the general usage is passing a lambda selector for the key and getting the object as the value, but you can pass a lambda selector for both key and value.

class SomeObject
{
    public int ID { get; set; }
    public string Name { get; set; }
}

SomeObject[] objects = new SomeObject[]
{
    new SomeObject { ID = 1, Name = "Hello" },
    new SomeObject { ID = 2, Name = "World" }
};

Dictionary<int, string> objectDictionary = objects.ToDictionary(o => o.ID, o => o.Name);

Then objectDictionary[1] Would contain the value "Hello"

User · Answer

var dictionary    from x in y                    select new SomeClass                                           prop1   value1                        prop2   value2                                         ToDictionary item   gt  item prop1     That s assuming that SomeClass prop1 is the desired Key for the dictionary

User · Answer

A more explicit option is to project collection to an IEnumerable of KeyValuePair and then convert it to a Dictionary  Dictionary lt int  string gt  dictionary   objects      Select x  gt  new KeyValuePair lt int  string gt  x Id  x Name        ToDictionary x  gt x Key  x  gt x Value

[c#] Select a Dictionary<T1, T2> with LINQ

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