Question

I’m looking for the shortest code to create methods to perform common operations on items in an IEnumerable.

For example:

public interface IPupil {     string Name { get; set; }     int Age { get; set; } } 

1. Summing a property – e.g. IPupil.Age in IEnumerable<IPupil>
2. Averaging a property – e.g. IPupil.Age in IEnumerable<IPupil>
3. Building a CSV string – e.g. IPupil.Name in IEnumerable<IPupil>

I’m interested in the various approaches to solve these examples: foreach (long hand), delegates, LINQ, anonymous methods, etc…

Sorry for the poor wording, I’m having trouble describing exactly what I’m after!

Answer 1

Summing and averaging: easy with LINQ:

var sum = pupils.Sum(pupil => pupil.Age); var average = pupils.Average(pupil => pupil.Age); 

Building a CSV string – there are various options here, including writing your own extension methods. This will work though:

var csv = string.Join(',', pupils.Select(pupil => pupil.Name).ToArray()); 

Note that it’s tricky to compute multiple things (e.g. average and sum) in one pass over the data with normal LINQ. If you’re interested in that, have a look at the Push LINQ project which Marc Gravell and I have written. It’s a pretty specialized requirement though.