Method WhereLead

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

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

Declaration

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

Parameters

Type	Name	Description
IEnumerable<TSource>	source	The sequence over which to evaluate Lead.
int	offset	The offset (expressed as a positive number) by which to lead each element of the sequence.
Func<TSource, TSource, bool>	predicate	A function which accepts the current and subsequent (lead) 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 lead value.

This operator evaluates in a deferred and streaming manner.

Examples

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

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

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

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

// This code produces the following output:
// [5, 6, 7, 8, 9, 10]

Exceptions

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

WhereLead<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 leading value.

Declaration

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

Parameters

Type	Name	Description
IEnumerable<TSource>	source	The sequence over which to evaluate Lead.
int	offset	The offset (expressed as a positive number) by which to lead each element of the sequence.
TSource	defaultLeadValue	A default value supplied for the leading element when none is available
Func<TSource, TSource, bool>	predicate	A function which accepts the current and subsequent (lead) 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 leading value in the sequence using WhereLead.

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

// Filter a sequence based on a leading value
var result = sequence
    .WhereLead(1, -20, (cur, lead) => cur + lead >= 10);

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

// This code produces the following output:
// [5, 6, 7, 8, 9]

Exceptions

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