MoreEnumerablePreScanTSource Method |
Performs a pre-scan (exclusive prefix sum) on a sequence of elements.
Namespace:
MoreLinq
Assembly:
MoreLinq (in MoreLinq.dll) Version: 2.4.0
Syntax public static IEnumerable<TSource> PreScan<TSource>(
this IEnumerable<TSource> source,
Func<TSource, TSource, TSource> transformation,
TSource identity
)
<ExtensionAttribute>
Public Shared Function PreScan(Of TSource) (
source As IEnumerable(Of TSource),
transformation As Func(Of TSource, TSource, TSource),
identity As TSource
) As IEnumerable(Of TSource)
public:
[ExtensionAttribute]
generic<typename TSource>
static IEnumerable<TSource>^ PreScan(
IEnumerable<TSource>^ source,
Func<TSource, TSource, TSource>^ transformation,
TSource identity
)
[<ExtensionAttribute>]
static member PreScan :
source : IEnumerable<'TSource> *
transformation : Func<'TSource, 'TSource, 'TSource> *
identity : 'TSource -> IEnumerable<'TSource>
Parameters
- source
- Type: System.Collections.GenericIEnumerableTSource
Source sequence - transformation
- Type: SystemFuncTSource, TSource, TSource
Transformation operation - identity
- Type: TSource
Identity element (see remarks)
Type Parameters
- TSource
- Type of elements in source sequence
Return Value
Type:
IEnumerableTSourceThe scanned sequence
Usage Note
In Visual Basic and C#, you can call this method as an instance method on any object of type
IEnumerableTSource. When you use instance method syntax to call this method, omit the first parameter. For more information, see
Extension Methods (Visual Basic) or
Extension Methods (C# Programming Guide).
Remarks
An exclusive prefix sum returns an equal-length sequence where the
N-th element is the sum of the first N-1 input elements (the first
element is a special case, it is set to the identity). More
generally, the pre-scan allows any commutative binary operation,
not just a sum.
The inclusive version of PreScan is
ScanTSource(IEnumerableTSource, FuncTSource, TSource, TSource).
This operator uses deferred execution and streams its result.
Examples Func<int, int, int> plus = (a, b) => a + b;
int[] values = { 1, 2, 3, 4 };
IEnumerable<int> prescan = values.PreScan(plus, 0);
IEnumerable<int> scan = values.Scan(plus; a + b);
IEnumerable<int> result = values.ZipShortest(prescan, plus);
prescan will yield
{ 0, 1, 3, 6 }, while
scan
and
result will both yield
{ 1, 3, 6, 10 }. This
shows the relationship between the inclusive and exclusive prefix sum.
See Also