math stats with Linq

Question

I have a collection of person objects (IEnumerable) and each person has an age property.

I want to generate stats on the collection such as Max, Min, Average, Median, etc on this age property.

What is the most elegant way of doing this using LINQ?

Answer 1

Here is a complete, generic implementation of Median that properly handles empty collections and nullable types. It is LINQ-friendly in the style of Enumerable.Average, for example:

    double? medianAge = people.Median(p => p.Age); 

This implementation returns null when there are no non-null values in the collection, but if you don't like the nullable return type, you could easily change it to throw an exception instead.

public static double? Median<TColl, TValue>(     this IEnumerable<TColl> source,     Func<TColl, TValue>     selector) {     return source.Select<TColl, TValue>(selector).Median(); }  public static double? Median<T>(     this IEnumerable<T> source) {     if(Nullable.GetUnderlyingType(typeof(T)) != null)         source = source.Where(x => x != null);      int count = source.Count();     if(count == 0)         return null;      source = source.OrderBy(n => n);      int midpoint = count / 2;     if(count % 2 == 0)         return (Convert.ToDouble(source.ElementAt(midpoint - 1)) + Convert.ToDouble(source.ElementAt(midpoint))) / 2.0;     else         return Convert.ToDouble(source.ElementAt(midpoint)); } 

Answer 2

var max = persons.Max(p => p.age); var min = persons.Min(p => p.age); var average = persons.Average(p => p.age); 

Fix for median in case of even number of elements

int count = persons.Count(); var orderedPersons = persons.OrderBy(p => p.age); float median = orderedPersons.ElementAt(count/2).age + orderedPersons.ElementAt((count-1)/2).age; median /= 2;