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 lt String  List lt Component gt  gt  dic   new Dictionary lt String  List lt Component gt  gt        Here I am trying to do the loping for List lt Component gt  foreach  List lt Component gt  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

User · Answer

You can do  Component depCountry   lstComp                         Select x   gt  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   gt  new                               Key   x Key                 Value   x Value Select  y   gt                                                     depCountry   y ComponentValue  Dep                            FirstOrDefault                                Where x   gt  x Value    null                ToDictionary x   gt  x Key  x   gt  x Value       This will give you a new dictionary   You can access the values   var myTest   newDictionary key1  depCountry

User · Answer

Try this to get all the list at first  then your desired element  say the First in your case    var desiredElementCompoundValueList   new List lt YourType gt     dic Values ToList   ForEach  elem   gt        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   gt  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

User · Answer

for the linq expression you can use like this     List lt int gt  list   new List lt int gt     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

User · Answer

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

User · Answer

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

User · Answer

0  or  First   will give you the same performance whatever happens  But your Dictionary could contains IEnumerable lt Component gt  instead of List lt Component gt   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 lt String  IEnumerable lt Component gt  gt     foreach  var components in dic Values           you can t use  0  because components is an IEnumerable lt Component gt      var firstComponent   components First       be aware that it will throw an exception if components is empty      var depCountry   firstComponent ComponentValue  Dep

User · Answer

I do so   List lt Object gt  list   new List lt Object gt      if list Count gt 0     Object obj   list 0

User · Answer

You also can use this   var firstOrDefault   lstComp FirstOrDefault    if firstOrDefault    null           doSmth

User · Answer

var firstObjectsOfValues    from d in dic select d Value 0  ComponentValue  Dep

User · Answer

I would to it like this     Dictionary object with Key as string and Value as List of Component type object Dictionary lt String  List lt Component gt  gt  dic   new Dictionary lt String  List lt Component gt  gt        from each element of the dictionary select first component if any IEnumerable lt Component gt  components   dic Where kvp   gt  kvp Value Any    Select kvp   gt   kvp Value First   as Component  ComponentValue  Dep       but only if it is sure that list contains only objects of Component class or children

[c#] How to get first object out from List<Object> using Linq

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