CODEWITHSUNDEEP
c#
user2740190
user2740190

Reputation:

Adding list of strings from one list to another list

I have one outer List BigList and then in my switch statements I have a bunch of other List smallerList variables. When I get to each of these cases in my switch I want to add those to the BigList But I also don't want to add repeated ones. How do we do that?

private List<string> MyMethod()
{
  List<string> BigList = null;
  for each( string name in MyListOfStringsThatComesIn)
  {
     tName = name;
     switch(tName)
     {
         case "dsdds":
            // List<string> smallerList;
            // add it to BigList
         case "fdfdf":
            // List<string> smallerList2;
            // add it to BigList
         case "vbbughb":
            // List<string> smallerList3;
            // add it to BigList

Upvotes: 2

Views: 1719

Answers (3)

Tim Schmelter
Tim Schmelter

Reputation: 460038

If duplicates aren't allowed i would use a HashSet<string> in the first place:

HashSet<string> bigSet = new HashSet<string>();
// add strings ...

If you want to add the whole List<string> into the set you can either use bigSet.Add in a loop or HashSet.UnionWith:

case "dsdds":
   bigSet.UnionWith(smallerList);

If you need to return a list you can use 

return new List<string>(bigSet);

Upvotes: 4

D Stanley
D Stanley

Reputation: 152501

Well, there's probably a more efficient way to do what you want, but based on what you have shown, you can either:

Look for strings that don;t exist in the parent list:

BigList.AddRange(smallerList.Except(BigList));

or just add them all (allowing duplicates) and call Distinct at the end:

BigList.AddRange(smallerList);
...
///add other lists


BigList = BigList.Distinct().ToList();

Also, you should probably intialize your list to an empty list rather then null:

List<string> BigList = new List<string>();

Upvotes: 1

Xiaoy312
Xiaoy312

Reputation: 14477

To create a new list based on the unique values of another one :

List<string> BigList = MyListOfStringsThatComesIn.Distinct().ToList();

To add new unique values from another list :

//assume the BigList contains something already...
BigList.AddRange(BigList.Except(MyListOfStringsThatComesIn));

Upvotes: 1

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