Get index of object in a list using Linq [duplicate]

Question

I am new to Linq. I have a Customers table.ID,FullName,Organization,Location being the columns. I have a query in Sqlite returning me 2500 records of customers. I have to find the index of the customer where ID=150 for example from this result set. Its a List of Customers. The result set of the query is ordered by organization. I tried with FindIndex and IndexOf but getting errors for the former and -1 for the latter. So, how should it be done? Thanks.

Plumlee

Answer 1

You don't need to use LINQ, you can use FindIndex of List<T>:

int index = customers.FindIndex(c => c.ID == 150);

Binocular

Nice, didn't know about this method – Primatology

Too bad this is not defined as a LINQ method and thus is only useful when working with a true pure List<T> rather than any IList<T>. – Trilbie

You have also Array.FindIndex<T>. – Binocular

@O.R.Mapper could apply this to most IEnumerables or ObservableCollections to a list by just using .ToList().FindIndex() – Plutonium

@Wilhelm: I rather dislike the idea of evaluating the entire enumeration if the element I'm looking for might be among the first couple of items. Also, note that there is never a good reason to use ToList() in situations where an array (as can be obtained from ToArray()) would do as well. – Trilbie

Answer 2

Linq to Objects has overloaded Select method

customers.Select((c,i) => new { Customer = c, Index = i })
         .Where(x => x.Customer.ID == 150)
         .Select(x => x.Index);

Keep in mind, that you should have in-memory List<Customer> to use this Linq to Objects method.

Primatology