How to get first object out from List<Object> using Linq

Question

I have below code in c# 4.0.

//Dictionary object with Key as string and Value as List of Component type object
Dictionary>         


        

Answer 1

[0] or .First() will give you the same performance whatever happens.
But your Dictionary could contains IEnumerable<Component> instead of List<Component>, and then you cant use the [] operator. That is where the difference is huge.

So for your example, it doesn't really matters, but for this code, you have no choice to use First():

var dic = new Dictionary<String, IEnumerable<Component>>();
foreach (var components in dic.Values)
{
    // you can't use [0] because components is an IEnumerable<Component>
    var firstComponent = components.First(); // be aware that it will throw an exception if components is empty.
    var depCountry = firstComponent.ComponentValue("Dep");
}

Answer 2

var firstObjectsOfValues = (from d in dic select d.Value[0].ComponentValue("Dep"));

Answer 3

There are a bunch of such methods:
.First .FirstOrDefault .Single .SingleOrDefault
Choose which suits you best.

Answer 4

for the linq expression you can use like this :

 List<int> list = new List<int>() {1,2,3 };
        var result = (from l in list
                     select l).FirstOrDefault();

for the lambda expression you can use like this

List list = new List() { 1, 2, 3 }; int x = list.FirstOrDefault();

Answer 5

Try:

var firstElement = lstComp.First();

You can also use FirstOrDefault() just in case lstComp does not contain any items.

http://msdn.microsoft.com/en-gb/library/bb340482(v=vs.100).aspx

Edit:

To get the Component Value:

var firstElement = lstComp.First().ComponentValue("Dep");

This would assume there is an element in lstComp. An alternative and safer way would be...

var firstOrDefault = lstComp.FirstOrDefault();
if (firstOrDefault != null) 
{
    var firstComponentValue = firstOrDefault.ComponentValue("Dep");
}

Answer 6

You also can use this:

var firstOrDefault = lstComp.FirstOrDefault();
if(firstOrDefault != null) 
{
    //doSmth
}