Method Lead

Lead<TSource>(IEnumerable<TSource>, int)

Produces a projection of a sequence by evaluating pairs of elements separated by a positive offset.

Declaration

public static IEnumerable<(TSource current, TSource? lead)> Lead<TSource>(this IEnumerable<TSource> source, int offset)

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

Returns

Type	Description
IEnumerable<(TSource current, TSource lag)>	A sequence of tuples with the current and lead elements

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 get elements along with a future value using Lead.

var sequence = new[] { "foo", "bar", "baz" };

// get leading elements
var result = sequence.Lead(1);

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

// This code produces the following output:
// [(foo, bar), (bar, baz), (baz, )]

Exceptions

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

Lead<TSource, TResult>(IEnumerable<TSource>, int, Func<TSource, TSource?, TResult>)

Produces a projection of a sequence by evaluating pairs of elements separated by a positive offset.

Declaration

public static IEnumerable<TResult> Lead<TSource, TResult>(this IEnumerable<TSource> source, int offset, Func<TSource, TSource?, TResult> resultSelector)

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, TResult>	resultSelector	A projection function which accepts the current and subsequent (lead) element (in that order) and produces a result

Returns

Type	Description
IEnumerable<TResult>	A sequence produced by projecting each element of the sequence with its lead pairing

Type Parameters

Name	Description
TSource	The type of the elements in the source sequence
TResult	The type of the elements in the result 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 get elements along with a future value using Lead.

var sequence = new[] { "foo", "bar", "baz" };

// get leading elements
var result = sequence.Lead(1, (cur, lead) => new { cur, lead, });

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

// This code produces the following output:
// [{ cur = foo, lead = bar }, { cur = bar, lead = baz }, { cur = baz, lead =  }]

Exceptions

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

Lead<TSource, TResult>(IEnumerable<TSource>, int, TSource, Func<TSource, TSource, TResult>)

Produces a projection of a sequence by evaluating pairs of elements separated by a positive offset.

Declaration

public static IEnumerable<TResult> Lead<TSource, TResult>(this IEnumerable<TSource> source, int offset, TSource defaultLeadValue, Func<TSource, TSource, TResult> resultSelector)

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, TResult>	resultSelector	A projection function which accepts the current and subsequent (lead) element (in that order) and produces a result

Returns

Type	Description
IEnumerable<TResult>	A sequence produced by projecting each element of the sequence with its lead pairing

Type Parameters

Name	Description
TSource	The type of the elements in the source sequence
TResult	The type of the elements in the result sequence

Remarks

For elements of the sequence that are less than offset items from the end, defaultLeadValue is used as the lead value.

This operator evaluates in a deferred and streaming manner.

Examples

The following code example demonstrates how to get elements along with a future value using Lead.

var sequence = new[] { "foo", "bar", "baz" };

// get leading elements
var result = sequence.Lead(1, "LEAD", (cur, lag) => new { cur, lag, });

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

// This code produces the following output:
// [{ cur = foo, lag = bar }, { cur = bar, lag = baz }, { cur = baz, lag = LEAD }]

Exceptions

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