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Comments on Update list based on presence of identifier in a second list
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Update list based on presence of identifier in a second list
In C#, I have two lists and need to mark records in the first based on the second. Here's a sample:
public class Vehicle
{
public string Make { get; set; }
public string VIN { get; set; }
public string Color { get; set; }
public bool HasRegistration { get; set; } = false;
}
The second list is simply a set of VINs (List<string>) that have been registered. I need to mark all the vehicles in the List<Vehicle> which have their VIN somewhere in the List<string>. This is what I have, and it works, but I am looking for something more LINQ.
foreach(var v in vehicles)
{
if (vinList.Contains(v.VIN))
{
v.HasRegistration = true;
}
}
I could also do v.HasRegistration = (vinList.Contains(v.VIN));
Can this be done in a single, LINQ statement?
Post
This can't be done with the standard library. It's quite common for people who want to do this to define their own extension method
public static void Foreach<T>(this IEnumerable<T> items, Action<T> action)
{
foreach (var item in items) action(item);
}
which would allow the one-liner
vehicles.Foreach(v => v.HasRegistration |= vinList.Contains(v.VIN));
There doesn't appear to be a consensus on whether this is an elegant and useful extension method or an abomination, so check your local style guide first.
Although it's not strictly an answer to the question, I must also point out that Contains on a list is a linear time operation, and unless you can guarantee that the list will never hold more than about three VINs you should first convert it to a data structure with a fast lookup. E.g.
var vinLookup = vinList.ToHashSet();
vehicles.Foreach(v => v.HasRegistration |= vinLookup.Contains(v.VIN));
If you don't have ToHashSet (in the standard library it's newish) then the implementation is just new HashSet<string>(vinList).
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