Method PreScan
| Edit this page View SourcePreScan<TSource>(IEnumerable<TSource>, Func<TSource, TSource, TSource>, TSource)
Performs a pre-scan (exclusive prefix sum) on a sequence of elements.
Declaration
public static IEnumerable<TSource> PreScan<TSource>(this IEnumerable<TSource> source, Func<TSource, TSource, TSource> transformation, TSource identity)Parameters
| Type | Name | Description |
|---|---|---|
| IEnumerable<TSource> | source | Source sequence |
| Func<TSource, TSource, TSource> | transformation | An accumulator function to be invoked on each element. |
| TSource | identity | The initial accumulator value. |
Returns
| Type | Description |
|---|---|
| IEnumerable<TSource> | The scanned sequence |
Type Parameters
| Name | Description |
|---|---|
| TSource | Type of elements in source sequence |
Remarks
An exclusive prefix scan returns an equal-length sequence where the N-th element is the aggregation of the
first N-1 input elements, where the first element is simply the identity value.
The inclusive version of PreScan is Scan<TSource>(IEnumerable<TSource>, Func<TSource, TSource, TSource>).
This operator uses deferred execution and streams its result.
Examples
The following code example demonstrates how to perform an exclusive pre-fix scan on a sequence using PreScan.
var sequence = Enumerable.Range(1, 4);
// execute a scan of the sequence, returning the aggregation before processing the element
var result = sequence.PreScan((a, b) => a + b, 0);
Console.WriteLine(
"[" +
string.Join(", ", result) +
"]");
// This code produces the following output:
// [0, 1, 3, 6]
Exceptions
| Type | Condition |
|---|---|
| ArgumentNullException |
|