Enumerable Extension Method to Distinct or Union IEnumerable(s) by a property without the need to create an IEqualityComparer<T> implementation.

EnumerableExtensions.cs

static class EnumerableExtensions
{
    public static IEnumerable<T> Distinct<T, TProperty>(
        this IEnumerable<T> source,
        Expression<Func<T, TProperty>> propertyExpression)
    {
        return source.Distinct(
            new PropertyExpressionComparer<T, TProperty>(propertyExpression));
    }

    public static IEnumerable<T> Union<T, TProperty>(
        this IEnumerable<T> first,
        IEnumerable<T> second,
        Expression<Func<T, TProperty>> propertyExpression)
    {
        return first.Union(
            second,
            new PropertyExpressionComparer<T, TProperty>(propertyExpression));
    }

    private class PropertyExpressionComparer<T, TProperty> : IEqualityComparer<T>
    {
        private readonly PropertyInfo _propertyInfo;

        public PropertyExpressionComparer(Expression<Func<T, TProperty>> propertyExpression)
        {
            string propertyName = ((MemberExpression)propertyExpression.Body).Member.Name;
            _propertyInfo = typeof(T).GetProperty(propertyName);
        }

        public bool Equals(T x, T y)
        {
            return _propertyInfo.GetValue(x).Equals(_propertyInfo.GetValue(y));
        }

        public int GetHashCode(T obj)
        {
            return _propertyInfo.GetValue(obj).GetHashCode();
        }
    }
}

example usage:

var res = from p in Process.GetProcesses()
          orderby p.ProcessName
          select p;

foreach (var item in res.Distinct(p => p.ProcessName))
{
    Console.WriteLine(item.ProcessName);
}

example usage:

var res = from p in Process.GetProcesses()
          orderby p.ProcessName
          select p;

foreach (var item in res.Distinct(p => p.ProcessName))
{
    Console.WriteLine(item.ProcessName);
}

example usage:

var res = from p in Process.GetProcesses()
          orderby p.ProcessName
          select p;

foreach (var item in res.Distinct(p => p.ProcessName))
{
    Console.WriteLine(item.ProcessName);
}

example usage:

var res = from p in Process.GetProcesses()
          orderby p.ProcessName
          select p;

foreach (var item in res.Distinct(p => p.ProcessName))
{
    Console.WriteLine(item.ProcessName);
}

example usage:

example usage:

var res = from p in Process.GetProcesses()
          orderby p.ProcessName
          select p;

foreach (var item in res.Distinct(p => p.ProcessName))
{
    Console.WriteLine(item.ProcessName);
}

example usage

var res = from p in Process.GetProcesses()
          orderby p.ProcessName
          select p;

foreach (var item in res.Distinct(p => p.ProcessName))
{
    Console.WriteLine(item.ProcessName);
}

usage:

var res = from p in Process.GetProcesses()
          orderby p.ProcessName
          select p;

foreach (var item in res.Distinct(p => p.ProcessName))
{
    Console.WriteLine(item.ProcessName);
}

var res = from p in Process.GetProcesses()
          orderby p.ProcessName
          select p;

foreach (var item in res.Distinct(p => p.ProcessName))
{
    Console.WriteLine(item.ProcessName);
}