How to get first object out from List

Question

I have below code in c# 4.0.

//Dictionary object with Key as string and Value as List of Component type object
Dictionary<String, List<Component>> dic = new Dictionary<String, List<Component>>();

//Here I am trying to do the loping for List<Component>
foreach (List<Component> lstComp in dic.Values.ToList())
{
    // Below I am trying to get first component from the lstComp object.
    // Can we achieve same thing using LINQ?
    // Which one will give more performance as well as good object handling?
    Component depCountry = lstComp[0].ComponentValue("Dep");
}

http://stackoverflow.com/questions/8886796/linq-firstordefault — Satpal, Apr 23 '13 at 08:13
How to check this condition Component depCountry = lstComp[0].ComponentValue("Dep"); getting first is easy how to get Component object from lstComp[0] component, so component is having component — Manoj Singh, Apr 23 '13 at 08:22
Also drop the `ToList()` on `Values` it's not needed and requires the creation of an extra object and an enumeration of the entire values collection. — Bob Vale, Apr 23 '13 at 09:15
Bob, what do you suggest instead of using ToList() as I need whole List object for doing the looping — Manoj Singh, Apr 23 '13 at 09:32

Darren · Accepted Answer · 2013-04-23T08:21:53.460

128

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");
}

edited Apr 23 '13 at 08:21

answered Apr 23 '13 at 08:13

Darren

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I need that component which is returned from .ComponentValue("Dep") field, that means lstComp[0] has got field which also contain component type of object – Manoj Singh Apr 23 '13 at 08:19
@ManojSingh - you can do lstComp.First().ComponentValue("Depature"); – Darren Apr 23 '13 at 08:21
1

Wouldn't `lstComp.Select(x => x.ComponentValue("Dep")).FirstOrDefault()` be better? (or even `(from x in lstComp select x.ComponentValue("Dep")).FirstOrDefault()`) – Bob Vale Apr 23 '13 at 08:44
1

@BobVale - I wouldn't necessarily say better, there are multiple ways to achieve the same result. However, I personally think the `.Select` with the lambda is not as easy to read as `.FirstOrDefault().` – Darren Apr 23 '13 at 08:49
Well apart from the fact that firstComponentValue is inaccessible outside the if statement, and you could end up with alot of nesting – Bob Vale Apr 23 '13 at 08:50
@BobVale - I edited my answer to show a safer practice, you could just use `First` as I also mention. However, If firstOrDefault is `null` you would not want to access `firstComponentValue` ..... – Darren Apr 23 '13 at 08:54
I suppose the main reason is OP asked for a LINQ answer and using the select statement is more LINQ – Bob Vale Apr 23 '13 at 09:17
@BobVale - .FirstOrDefault is `LINQ` too. Using an unnecessary `Select`, `Lambda`, `from`, `in` clause does not make it `More LINQ` – Darren Apr 23 '13 at 09:22
The `if` statement is what I was referring to, also the use of the select allows the possibility of creating an anonymous type for a return value if more than one property is needed. – Bob Vale Apr 23 '13 at 09:24
@BobVale - but the OP wanted the ComponentValue("Dep") value, you can actually see him stating this in the in the comments. What are you trying to achieve by rambling on here? – Darren Apr 23 '13 at 09:26

Cyril Gandon · Answer 2 · 2013-04-23T09:10:53.277

[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");
}

Why the ToList() on the Values? – Bob Vale Apr 23 '13 at 09:08 — Bob Vale, Apr 23 '13 at 09:08

score 1 · Answer 3 · answered Apr 23 '13 at 08:15

1

You also can use this:

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

answered Apr 23 '13 at 08:15

Andrei

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Francesco De Lisi · Answer 4 · 2013-04-23T09:49:10.963

1

Try this to get all the list at first, then your desired element (say the First in your case):

var desiredElementCompoundValueList = new List<YourType>();
dic.Values.ToList().ForEach( elem => 
{
   desiredElementCompoundValue.Add(elem.ComponentValue("Dep"));
});
var x = desiredElementCompoundValueList.FirstOrDefault();

To get directly the first element value without a lot of foreach iteration and variable assignment:

var desiredCompoundValue = dic.Values.ToList().Select( elem => elem.CompoundValue("Dep")).FirstOrDefault();

See the difference between the two approaches: in the first one you get the list through a ForEach, then your element. In the second you can get your value in a straight way.

Same result, different computation ;)

edited Apr 23 '13 at 09:49

answered Apr 23 '13 at 08:30

Francesco De Lisi

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Both of these answers require an enumeration of the entire collection of values due to the use of `ToList()` – Bob Vale Apr 23 '13 at 09:07
Sure, I assume it's correct because he's using a Dictionary of List without performace issues. The difference is in the cycle, the second solution is better to me. Modifying his code to fit with a "lighter" one is a loss of time in this case, even if I agree with a better way to store in memory infos. I see at least 2 classes with properties to represent the whole behaviour! Regards. – Francesco De Lisi Apr 23 '13 at 09:22
Won't the second example fail. The parameter to `FirstOrDefault` expects a filter function that returns a bool, not a select function – Bob Vale Apr 23 '13 at 09:27
Ooops, I miss the Select and the first is totally wrong! Thank you, I will fix it! – Francesco De Lisi Apr 23 '13 at 09:36
Other way round, select before FirstOrDefault – Bob Vale Apr 23 '13 at 09:37
1

Return type of FirstOrDefault is single object, not IEnumerable – Bob Vale Apr 23 '13 at 09:47

score 1 · Answer 5 · answered Apr 23 '13 at 08:47

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();

score 1 · Answer 6 · answered Apr 23 '13 at 08:58

You can do

Component depCountry = lstComp
                       .Select(x => x.ComponentValue("Dep"))
                       .FirstOrDefault();

Alternatively if you are wanting this for the entire dictionary of values, you can even tie it back to the key

var newDictionary = dic.Select(x => new 
            {
               Key = x.Key,
               Value = x.Value.Select( y => 
                      {
                          depCountry = y.ComponentValue("Dep")
                      }).FirstOrDefault()
             }
             .Where(x => x.Value != null)
             .ToDictionary(x => x.Key, x => x.Value());

This will give you a new dictionary. You can access the values

var myTest = newDictionary[key1].depCountry

score 0 · Answer 7 · answered Apr 23 '13 at 08:14

0

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

answered Apr 23 '13 at 08:14

Vladimir

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@jle No, it'll return an `IEnumerable`. – ken2k Apr 23 '13 at 08:24
it would only contain the first element, but I suppose it would not be the 'first object' per the OP's question – jle Apr 23 '13 at 08:28
@jle `Take()` returns an enumeration without actual execution, so you'll still have to use either `.ToList()`, `First`, `Single`, `FirstOrDefault`...etc. to actually execute the query. – ken2k Apr 23 '13 at 08:38

score 0 · Answer 8 · answered Apr 23 '13 at 08:27

0

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

answered Apr 23 '13 at 08:27

Victor Mukherjee

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Sarrus · Answer 9 · 2013-04-23T08:50:47.830

0

I would to it like this:

//Dictionary object with Key as string and Value as List of Component type object
Dictionary<String, List<Component>> dic = new Dictionary<String, List<Component>>();

//from each element of the dictionary select first component if any
IEnumerable<Component> components = dic.Where(kvp => kvp.Value.Any()).Select(kvp => (kvp.Value.First() as Component).ComponentValue("Dep"));

but only if it is sure that list contains only objects of Component class or children

edited Apr 23 '13 at 08:50

answered Apr 23 '13 at 08:39

Sarrus

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It can only have Component or its children because you've defined the dictioanry that way! – Bob Vale Apr 23 '13 at 09:08
Yes I have, in my example. Just feel a need to leave a note, because improper use of `as` operator in linq statement is dangerous and may be cause of application crash. But you're right - it's obvious in this case. – Sarrus Apr 23 '13 at 13:58

How to get first object out from List

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