/// <summary>
/// Continual computes the sum of values matching the value selector.
/// </summary>
/// <typeparam name="T">The type of the item.</typeparam>
/// <param name="source">The source.</param>
/// <param name="valueSelector">The value selector.</param>
/// <returns>An observable which emits the summed value.</returns>
public static IObservable <decimal> Sum <T>(this IObservable <IAggregateChangeSet <T> > source, Func <T, decimal> valueSelector)
{
if (source is null)
{
throw new ArgumentNullException(nameof(source));
}
if (valueSelector is null)
{
throw new ArgumentNullException(nameof(valueSelector));
}
return(source.Accumulate(0, valueSelector, (current, value) => current + value, (current, value) => current - value));
}
/// <summary>
/// Continual computes the sum of values matching the value selector.
/// </summary>
/// <typeparam name="T">The type of the item.</typeparam>
/// <param name="source">The source.</param>
/// <param name="valueSelector">The value selector.</param>
/// <returns>An observable which emits the summed value.</returns>
public static IObservable <float> Sum <T>(this IObservable <IAggregateChangeSet <T> > source, Func <T, float?> valueSelector)
{
if (source is null)
{
throw new ArgumentNullException(nameof(source));
}
if (valueSelector is null)
{
throw new ArgumentNullException(nameof(valueSelector));
}
return(source.Accumulate(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>An observable which emits the count.</returns>
public static IObservable <int> Count <TObject>(this IObservable <IAggregateChangeSet <TObject> > source)
{
return(source.Accumulate(0, _ => 1, (current, increment) => current + increment, (current, increment) => current - increment));
}
/// <summary>
/// Continual computes the sum of values matching the value selector.
/// </summary>
/// <typeparam name="T">The type of the item.</typeparam>
/// <param name="source">The source.</param>
/// <param name="valueSelector">The value selector.</param>
/// <returns>An observable which emits the summed value.</returns>
public static IObservable <int> Sum <T>(this IObservable <IAggregateChangeSet <T> > source, Func <T, int?> valueSelector)
{
return(source.Accumulate(0, t => valueSelector(t).GetValueOrDefault(), (current, value) => current + value, (current, value) => current - value));
}
