Welcome to Software Development on Codidact!
Will you help us build our independent community of developers helping developers? We're small and trying to grow. We welcome questions about all aspects of software development, from design to code to QA and more. Got questions? Got answers? Got code you'd like someone to review? Please join us.
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?
3 answers
You are accessing this answer with a direct link, so it's being shown above all other answers regardless of its score. You can return to the normal view.
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).
1 comment thread
If you want to be more Linq-like without creating a ForEach method:
vehicles = vehicles
.Select(
v =>
new Vehicle
{
Make = v.Make,
VIN = v.VIN,
Color = v.Color,
HsRegistration = vinList.Contains(v.VIN)
}
).ToList();
Here we're treating Vehicle and the list like immutable objects, and creating modified copies rather than mutating them.
Can you make Vehicle a record rather than a class?
record VehicleRecord
{
internal string Make;
internal string VIN;
internal string Color;
internal bool HasRegistration;
}
If so you can simplify this to:
vehicles = vehicles
.Select(
v => v with { HasRegistration = vinList.Contains(v.VIN) }
).ToList();
0 comment threads
Adding to Peter Taylor's reply:
The OP requested something "more LINQ". I guess it can't get any "more linq" than... MoreLINQ!
That library also has a ForEach().
If you only need that, maybe it's a bit much to use that lib, but if you like the other stuff in there, too, which I suspect... Was not the question, but hint anyway: their MaxBy, MinBy functions are neat.
0 comment threads
1 comment thread