convert a list of objects from one type to another using lambda expression

Question

I have a foreach loop reading a list of objects of one type and producing a list of objects of a different type. I was told that a lambda expression can achieve the same result.

var origList = List<OrigType>(); // assume populated var targetList = List<TargetType>();   foreach(OrigType a in origList) {     targetList.Add(new TargetType() {SomeValue = a.SomeValue}); } 

Any help would be appreciated- i'm new to lambda and linq thanks, s

Answer 1

Try the following

var targetList = origList   .Select(x => new TargetType() { SomeValue = x.SomeValue })   .ToList(); 

This is using a combination of Lambdas and LINQ to achieve the solution. The Select function is a projection style method which will apply the passed in delegate (or lambda in this case) to every value in the original collection. The result will be returned in a new IEnumerable<TargetType>. The .ToList call is an extension method which will convert this IEnumerable<TargetType> into a List<TargetType>.

Answer 2

If you know you want to convert from List<T1> to List<T2> then List<T>.ConvertAll will be slightly more efficient than Select/ToList because it knows the exact size to start with:

target = orig.ConvertAll(x => new TargetType { SomeValue = x.SomeValue }); 

In the more general case when you only know about the source as an IEnumerable<T>, using Select/ToList is the way to go. You could also argue that in a world with LINQ, it's more idiomatic to start with... but it's worth at least being aware of the ConvertAll option.