Method Flatten

Flatten(IEnumerable)

Flattens a sequence containing arbitrarily-nested sequences.

Declaration

public static IEnumerable<object?> Flatten(this IEnumerable source)

Parameters

Type	Name	Description
IEnumerable	source	The sequence that will be flattened.

Returns

Type	Description
IEnumerable<object>	A sequence that contains the elements of source and all nested sequences (except strings).

Remarks

This method uses deferred execution and streams its results.

Examples

The following code example demonstrates how to flatten hierarchical sequences into a flat sequences using Flatten.

var sequence = new object[]
{
    1, 2, 3,
    new object[]
    {
        4, 5,
        new object[] { 6, 7, },
        8, 9, 10, 
    },
    11,
    new object[]
    {
        12, 13, 14,
        new object[] { 15, 16, 17, },
        18, 19,
    },
    20,
};

// Flatten a hierarchical sequence
var result = sequence.Flatten();

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

// This code produces the following output:
// [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]

Exceptions

Type	Condition
ArgumentNullException	source is null.

Flatten(IEnumerable, Func<IEnumerable, bool>)

Flattens a sequence containing arbitrarily-nested sequences. An additional parameter specifies a predicate function used to determine whether a nested IEnumerable should be flattened or not.

Declaration

public static IEnumerable<object?> Flatten(this IEnumerable source, Func<IEnumerable, bool> predicate)

Parameters

Type	Name	Description
IEnumerable	source	The sequence that will be flattened.
Func<IEnumerable, bool>	predicate	A function that receives each element that implements IEnumerable and indicates if its elements should be recursively flattened into the resulting sequence.

Returns

Type	Description
IEnumerable<object>	A sequence that contains the elements of source and all nested sequences for which the predicate function returned true.

Remarks

This method uses deferred execution and streams its results.

Examples

The following code example demonstrates how to flatten hierarchical sequences into a flat sequences using Flatten.

var sequence = new object[]
{
    1, 2, 3,
    new object[]
    {
        4, 5,
        new int[] { 6, 7, 8, },
    },
    9, 10, 11,
    new object[]
    {
        12, 13, 14,
        new object[] { 15, 16, 17, },
        18, 19,
    },
    20,
};

// Flatten a hierarchical sequence
var result = sequence
    .Flatten(e => e is not int[]);

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

// This code produces the following output:
// [1, 2, 3, 4, 5, System.Int32[], 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]

Exceptions

Type	Condition
ArgumentNullException	source or predicate is null.

Flatten(IEnumerable, Func<object?, IEnumerable?>)

Flattens a sequence containing arbitrarily-nested sequences. An additional parameter specifies a function that projects an inner sequence via a property of an object.

Declaration

public static IEnumerable<object?> Flatten(this IEnumerable source, Func<object?, IEnumerable?> selector)

Parameters

Type	Name	Description
IEnumerable	source	The sequence that will be flattened.
Func<object, IEnumerable>	selector	A function that receives each element of the sequence as an object and projects an inner sequence to be flattened. If the function returns null then the object argument is considered a leaf of the flattening process.

Returns

Type	Description
IEnumerable<object>	A sequence that contains the elements of source and all nested sequences projected via the selector function.

Remarks

This method uses deferred execution and streams its results.

Examples

The following code example demonstrates how to flatten hierarchical sequences into a flat sequences using Flatten.

var sequence = new object[]
{
    true,
    false,
    1,
    "bar",
    new object[]
    {
        2,
        new[]
        {
            3,
        },
    },
    'c',
    4,
};

// Flatten a hierarchical sequence
var result = sequence
    .Flatten(obj =>
        obj switch
        {
            int => null,
            IEnumerable inner => inner,
            _ => Enumerable.Empty<object>(),
        });

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

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

Exceptions

Type	Condition
ArgumentNullException	source or selector is null.