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How can I find a specific element in a List<T>?
8 answers
Suppose we have a class called Dog with two strings "Name" and "Id". Now suppose we have a list with 4 dogs in it. If you wanted to change the name of the Dog with the "Id" of "2" what would be the best way to do it?
Dog d1 = new Dog("Fluffy", "1");
Dog d2 = new Dog("Rex", "2");
Dog d3 = new Dog("Luna", "3");
Dog d4 = new Dog("Willie", "4");
List<Dog> AllDogs = new List<Dog>()
AllDogs.Add(d1);
AllDogs.Add(d2);
AllDogs.Add(d3);
AllDogs.Add(d4);
AllDogs.First(d => d.Id == "2").Name = "some value";
However, a safer version of that might be this:
var dog = AllDogs.FirstOrDefault(d => d.Id == "2");
if (dog != null) { dog.Name = "some value"; }
You could do:
var matchingDog = AllDogs.FirstOrDefault(dog => dog.Id == "2"));
This will return the matching dog, else it will return null
.
You can then set the property like follows:
if (matchingDog != null)
matchingDog.Name = "New Dog Name";
If the list is sorted (as happens to be in the example) a binary search on index certainly works.
public static Dog Find(List<Dog> AllDogs, string Id)
{
int p = 0;
int n = AllDogs.Count;
while (true)
{
int m = (n + p) / 2;
Dog d = AllDogs[m];
int r = string.Compare(Id, d.Id);
if (r == 0)
return d;
if (m == p)
return null;
if (r < 0)
n = m;
if (r > 0)
p = m;
}
}
Not sure what the LINQ version of this would be.