Method Lag
| Edit this pageLag<TSource>(IEnumerable<TSource>, int)
Produces a projection of a sequence by evaluating pairs of elements separated by a negative offset.
Declaration
public static IEnumerable<(TSource current, TSource? lag)> Lag<TSource>(this IEnumerable<TSource> source, int offset)Parameters
| Type | Name | Description |
|---|---|---|
| IEnumerable<TSource> | source | The sequence over which to evaluate lag |
| int | offset | The offset (expressed as a positive number) by which to lag each value of the sequence |
Returns
| Type | Description |
|---|---|
| IEnumerable<(TSource current, TSource lag)> | A sequence of tuples with the current and lagged elements |
Type Parameters
| Name | Description |
|---|---|
| TSource | The type of the elements of the source sequence |
Remarks
For elements prior to the lag offset, default( is
used as the lagged value.TSource?)
This operator evaluates in a deferred and streaming manner.
Examples
The following code example demonstrates how to get elements along with a previous value using Lag.
var sequence = new[] { "foo", "bar", "baz" };
// get lagged elements
var result = sequence.Lag(1);
Console.WriteLine(
"[" +
string.Join(", ", result) +
"]");
// This code produces the following output:
// [(foo, ), (bar, foo), (baz, bar)]
Exceptions
| Type | Condition |
|---|---|
| ArgumentNullException |
|
| ArgumentOutOfRangeException |
|
Lag<TSource, TResult>(IEnumerable<TSource>, int, Func<TSource, TSource?, TResult>)
Produces a projection of a sequence by evaluating pairs of elements separated by a negative offset.
Declaration
public static IEnumerable<TResult> Lag<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 lag |
| int | offset | The offset (expressed as a positive number) by which to lag each value of the sequence |
| Func<TSource, TSource, TResult> | resultSelector | A projection function which accepts the current and lagged items (in that order) and returns a result |
Returns
| Type | Description |
|---|---|
| IEnumerable<TResult> | A sequence produced by projecting each element of the sequence with its lagged pairing |
Type Parameters
| Name | Description |
|---|---|
| TSource | The type of the elements of the source sequence |
| TResult | The type of the elements of the result sequence |
Remarks
For elements prior to the lag offset, default( is
used as the lagged value.TSource?)
This operator evaluates in a deferred and streaming manner.
Examples
The following code example demonstrates how to get elements along with a previous value using Lag.
var sequence = new[] { "foo", "bar", "baz" };
// get lagged elements
var result = sequence.Lag(1, (cur, lag) => new { cur, lag, });
Console.WriteLine(
"[" +
string.Join(", ", result) +
"]");
// This code produces the following output:
// [{ cur = foo, lag = }, { cur = bar, lag = foo }, { cur = baz, lag = bar }]
Exceptions
| Type | Condition |
|---|---|
| ArgumentNullException |
|
| ArgumentOutOfRangeException |
|
Lag<TSource, TResult>(IEnumerable<TSource>, int, TSource, Func<TSource, TSource, TResult>)
Produces a projection of a sequence by evaluating pairs of elements separated by a negative offset.
Declaration
public static IEnumerable<TResult> Lag<TSource, TResult>(this IEnumerable<TSource> source, int offset, TSource defaultLagValue, Func<TSource, TSource, TResult> resultSelector)Parameters
| Type | Name | Description |
|---|---|---|
| IEnumerable<TSource> | source | The sequence over which to evaluate lag |
| int | offset | The offset (expressed as a positive number) by which to lag each value of the sequence |
| TSource | defaultLagValue | A default value supplied for the lagged value prior to the lag offset |
| Func<TSource, TSource, TResult> | resultSelector | A projection function which accepts the current and lagged items (in that order) and returns a result |
Returns
| Type | Description |
|---|---|
| IEnumerable<TResult> | A sequence produced by projecting each element of the sequence with its lagged pairing |
Type Parameters
| Name | Description |
|---|---|
| TSource | The type of the elements of the source sequence |
| TResult | The type of the elements of the result sequence |
Remarks
For elements prior to the lag offset, defaultLagValue is used as the lagged value.
This operator evaluates in a deferred and streaming manner.
Examples
The following code example demonstrates how to get elements along with a previous value using Lag.
var sequence = new[] { "foo", "bar", "baz" };
// get lagged elements
var result = sequence.Lag(1, "LAG", (cur, lag) => new { cur, lag, });
Console.WriteLine(
"[" +
string.Join(", ", result) +
"]");
// This code produces the following output:
// [{ cur = foo, lag = LAG }, { cur = bar, lag = foo }, { cur = baz, lag = bar }]
Exceptions
| Type | Condition |
|---|---|
| ArgumentNullException |
|
| ArgumentOutOfRangeException |
|