Question

I have a list of ProjectItem class instances: List<ProjectItem> allProjects.

I need to obtain a List<ProjectItemPair> – a list of new class instances, that have ProjectItem projectOne and ProjectItem projectTwo as a properties.

I had to foreach the initial list, and using a bool switch was adding a new ProjectItemPair into a resulting list on every second item in iteration. This is a primitive old school approach. I am sure with Linq I can pair the project instances up effectively. How can I do it?

Answer 1

Well, you could use:

var pairs = allProjects.Select((value, index) = > new { value, index })
                       .GroupBy(x => x.index / 2, x => x.value)
                       .Select(pair => new ProjectItemPair(pair.ElementAt(0),
                                                     pair.ElementAtOrDefault(1)))
                       .ToList();

The use of ElementAtOrDefault means the constructor will be passed null if there’s an odd number of elements.

Another somewhat simpler alternative:

var pairs = Enumerable.Range(0, allProjects.Count / 2)
                      .Select(i => new ProjectItemPair(allProjects[i * 2],
                                                       allProjects[i * 2 + 1]))
                      .ToList();

This will omit the final element if the input has an odd number of elements, in which case you can do:

if ((allProjects.Count % 2) == 1)
{
    pairs.Add(new ProjectItemPair(allProjects.Last(), null);
}