/// <summary>
/// Continual computes the sum of values matching the value selector
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="source">The source.</param>
/// <param name="valueSelector">The value selector.</param>
/// <returns></returns>
public static IObservable <int> Sum <T>([NotNull] this IObservable <IAggregateChangeSet <T> > source, [NotNull] Func <T, int?> valueSelector)
{
return(source.Accumlate(0,
t => valueSelector(t).GetValueOrDefault(),
(current, value) => current + value,
(current, value) => current - value));
}
/// <summary>
/// Continual computes the sum of values matching the value selector
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="source">The source.</param>
/// <param name="valueSelector">The value selector.</param>
/// <returns></returns>
public static IObservable <float> Sum <T>([NotNull] this IObservable <IAggregateChangeSet <T> > source, [NotNull] Func <T, float?> valueSelector)
{
if (source == null)
{
throw new ArgumentNullException(nameof(source));
}
if (valueSelector == null)
{
throw new ArgumentNullException(nameof(valueSelector));
}
return(source.Accumlate(0F,
t => valueSelector(t).ValueOr(0),
(current, value) => current + value,
(current, value) => current - value));
}
/// <summary>
/// Counts the total number of items in the underlying data source
/// </summary>
/// <typeparam name="TObject">The type of the object.</typeparam>
/// <param name="source">The source.</param>
/// <returns></returns>
public static IObservable <int> Count <TObject>(this IObservable <IAggregateChangeSet <TObject> > source)
{
return(source.Accumlate(0, t => 1,
(current, increment) => current + increment,
(current, increment) => current - increment));
}
