Method WhereLag

WhereLag<TSource>(IEnumerable<TSource>, int, Func<TSource, TSource?, bool>)

Filters a sequence of values based on a predicate evaluated on the current value and a lagging value.

Declaration

public static IEnumerable<TSource> WhereLag<TSource>(this IEnumerable<TSource> source, int offset, Func<TSource, TSource?, bool> predicate)

Parameters

Type	Name	Description
IEnumerable<TSource>	source	An IEnumerable<T> to filter.
int	offset	The offset (expressed as a positive number) by which to lag each element of the sequence.
Func<TSource, TSource, bool>	predicate	A function which accepts the current and lagged element (in that order) to test for a condition.

Returns

Type	Description
IEnumerable<TSource>	An IEnumerable<T> that contains elements from the input sequence that satisfy the condition.

Type Parameters

Name	Description
TSource	The type of the elements in the source sequence.

Remarks

For elements of the sequence that are less than offset items from the end, default(TSource?) is used as the Lag value.

This operator evaluates in a deferred and streaming manner.

Examples

The following code example demonstrates how to filter a sequence based on a lagging value in the sequence using WhereLag.

var sequence = Enumerable.Range(1, 10);

// Filter a sequence based on a leading value
var result = sequence
    .WhereLag(1, (cur, lag) => cur + lag < 10);

Console.WriteLine(
    "[" +
    string.Join(", ", result) +
    "]");

// This code produces the following output:
// [1, 2, 3, 4, 5]

Exceptions

Type	Condition
ArgumentNullException	source or predicate is null.
ArgumentOutOfRangeException	offset is below 1.

WhereLag<TSource>(IEnumerable<TSource>, int, TSource, Func<TSource, TSource, bool>)

Filters a sequence of values based on a predicate evaluated on the current value and a lagging value.

Declaration

public static IEnumerable<TSource> WhereLag<TSource>(this IEnumerable<TSource> source, int offset, TSource defaultLagValue, Func<TSource, TSource, bool> predicate)

Parameters

Type	Name	Description
IEnumerable<TSource>	source	An IEnumerable<T> to filter.
int	offset	The offset (expressed as a positive number) by which to lag each element of the sequence.
TSource	defaultLagValue	A default value supplied for the lagged element when none is available
Func<TSource, TSource, bool>	predicate	A function which accepts the current and lagged element (in that order) to test for a condition.

Returns

Type	Description
IEnumerable<TSource>	An IEnumerable<T> that contains elements from the input sequence that satisfy the condition.

Type Parameters

Name	Description
TSource	The type of the elements in the source sequence.

Remarks

This operator evaluates in a deferred and streaming manner.

Examples

The following code example demonstrates how to filter a sequence based on a lagging value in the sequence using WhereLag.

var sequence = Enumerable.Range(1, 10);

// Filter a sequence based on a leading value
var result = sequence
    .WhereLag(1, 20, (cur, lag) => cur + lag < 10);

Console.WriteLine(
    "[" +
    string.Join(", ", result) +
    "]");

// This code produces the following output:
// [2, 3, 4, 5]

Exceptions

Type	Condition
ArgumentNullException	source or predicate is null.
ArgumentOutOfRangeException	offset is below 1.