Method BindByIndex

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

Selects elements by index from a sequence.

Declaration
public static IEnumerable<TSource> BindByIndex<TSource>(this IEnumerable<TSource> source, IEnumerable<int> indices)
Parameters
Type Name Description
IEnumerable<TSource> source

The source sequence.
IEnumerable<int> indices

The list of indices of elements in the source sequence to select.
Returns
Type Description
IEnumerable<TSource>

An IEnumerable<T> whose elements are the result of selecting elements according to the indices sequence.
Type Parameters
Name Description
TSource

The type of the elements of source.
Remarks

This operator uses deferred execution and streams its results.

Examples

The following code example demonstrates how to select elements from a sequence by index, using BindByIndex.

var sequence = Enumerable.Range(1, 10);
var indices = new int[] { 0, 1, 8, 9, 3, 4, 2, };

// Select elements from sequence using the values in indices
var result = sequence
    .BindByIndex(indices);

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

// This code produces the following output:
// [1, 2, 9, 10, 4, 5, 3]
Exceptions
Type Condition
ArgumentNullException

source or indices is null.
ArgumentOutOfRangeException

(Thrown lazily) An index in indices is out of range for the input sequence source.
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BindByIndex<TSource, TResult>(IEnumerable<TSource>, IEnumerable<int>, Func<TSource, int, TResult>, Func<int, TResult>)

Selects elements by index from a sequence and transforms them using the provided functions.

Declaration
public static IEnumerable<TResult> BindByIndex<TSource, TResult>(this IEnumerable<TSource> source, IEnumerable<int> indices, Func<TSource, int, TResult> resultSelector, Func<int, TResult> missingSelector)
Parameters
Type Name Description
IEnumerable<TSource> source

The source sequence.
IEnumerable<int> indices

The list of indices of elements in the source sequence to select.
Func<TSource, int, TResult> resultSelector

A transform function to apply to each source element; the second parameter of the function represents the index of the output sequence.
Func<int, TResult> missingSelector

A transform function to apply to missing source elements; the parameter represents the index of the output sequence.
Returns
Type Description
IEnumerable<TResult>

An IEnumerable<T> whose elements are the result of selecting elements according to the indices sequence and invoking the transform function.
Type Parameters
Name Description
TSource

The type of the elements of source.
TResult

The type of the elements of the resulting sequence.
Remarks

This operator uses deferred execution and streams its results.

Examples

The following code example demonstrates how to select elements from a sequence by index, using BindByIndex.

var sequence = Enumerable.Range(1, 10);
var indices = new int[] { 0, 1, 8, 10, 3, 4, 2, };

// Select elements from sequence using the values in indices
var result = sequence
    .BindByIndex(
        indices,
        (e, i) => e.ToString(),
        i => "null");

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

// This code produces the following output:
// [1, 2, 9, null, 4, 5, 3]
Exceptions
Type Condition
ArgumentNullException

source, indices, resultSelector, or missingSelector is null.