LINQ select one field from list of DTO objects to array

Question

I have DTO class that defines order line like this   public class Line       public string Sku   get  set        public int Qty      get  set        A list of type Line is populated like so   List lt Line gt  myLines   new List lt Line gt     myLines Add new Line     Sku    ABCD1   Qty   1     myLines Add new Line     Sku    ABCD2   Qty   1     myLines Add new Line     Sku    ABCD3   Qty   1       What I want is to use LINQ to get an array of SKUs from the myLines List  How can I go about doing that   I am currently doing it manually like this         Get SKU List List lt string gt  mySKUs   new List lt string gt     foreach  Line myLine in myLines      mySKUs Add myLine Sku   string   mySKUsArray   mySKUs ToArray      Thanks in advance  I was trying to google for a solution  but I wasn t sure how to word the question     P S  is there any benefit performance gain in using LINQ method to achieve what I am currently doing with foreach

User · Answer

I think you re looking for     string   skus   myLines Select x   gt  x Sku  ToArray      However  if you re going to iterate over the sku s in subsequent code I recommend not using the ToArray   bit as it forces the queries execution prematurely and makes the applications performance worse  Instead you can just do     var skus   myLines Select x   gt  x Sku      produce IEnumerable lt string gt     foreach  string sku in skus     forces execution of the query

User · Answer

You can select all Sku elements of your myLines list and then convert the result to an array   string   mySKUsArray   myLines Select x  gt x Sku  ToArray

User · Answer

You can use   var mySKUs   myLines Select l   gt  l Sku  ToList      The Select method  in this case  performs a mapping from IEnumerable lt Line gt  to IEnumerable lt string gt   the SKU   then ToList   converts it to a List lt string gt    Note that this requires using System Linq  to be at the top of your  cs file

User · Answer

In the case you re interested in extremely minor  almost immeasurable performance increases  add a constructor to your Line class  giving you such   public class Line       public Line string sku  int qty                this Sku   sku          this Qty   qty             public string Sku   get  set        public int Qty      get  set        Then create a specialized collection class based on List lt Line gt  with one new method  Add   public class LineList   List lt Line gt        public void Add string sku  int qty                this Add new Line sku  qty              Then the code which populates your list gets a bit less verbose by using a collection initializer   LineList myLines   new LineList          ABCD1   1           ABCD2   1           ABCD3   1        And  of course  as the other answers state  it s trivial to extract the SKUs into a string array with LINQ   string   mySKUsArray   myLines Select myLine   gt  myLine Sku  ToArray

User · Answer

This is very simple in LinQ    You can use the select statement to get an Enumerable of properties of the objects   var mySkus   myLines Select x   gt  x Sku     Or if you want it as an Array just do     var mySkus   myLines Select x   gt  x Sku  ToArray

[c#] LINQ select one field from list of DTO objects to array

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