Method Fold

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Fold<T, TResult>(IEnumerable<T>, Func<T, TResult>)

Returns the result of applying a function to a sequence of 1 element.

Declaration
public static TResult Fold<T, TResult>(this IEnumerable<T> source, Func<T, TResult> folder)
Parameters
Type Name Description
IEnumerable<T> source

The sequence of items to fold.
Func<T, TResult> folder

Function to apply to the elements in the sequence.
Returns
Type Description
TResult

The folded value returned by folder.
Type Parameters
Name Description
T

Type of element in the source sequence
TResult

Type of the result
Remarks

This operator uses immediate execution and buffers as many items of the source sequence as necessary.

Examples

The following code example demonstrates how to apply a projection to a sequence of 1 element using Fold.

var sequence = Enumerable.Range(1, 1);
            
// Fold a sequence into a single value.
var result = sequence
    .Fold((a) => a);

Console.WriteLine(result);

// This code produces the following output:
// 1
Exceptions
Type Condition
ArgumentNullException

source or folder is null.
InvalidOperationException

source does not contain exactly 1 element.
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Fold<T, TResult>(IEnumerable<T>, Func<T, T, TResult>)

Returns the result of applying a function to a sequence of 2 elements.

Declaration
public static TResult Fold<T, TResult>(this IEnumerable<T> source, Func<T, T, TResult> folder)
Parameters
Type Name Description
IEnumerable<T> source

The sequence of items to fold.
Func<T, T, TResult> folder

Function to apply to the elements in the sequence.
Returns
Type Description
TResult

The folded value returned by folder.
Type Parameters
Name Description
T

Type of element in the source sequence
TResult

Type of the result
Remarks

This operator uses immediate execution and buffers as many items of the source sequence as necessary.

Examples

The following code example demonstrates how to apply a projection to a sequence of 2 elements using Fold.

var sequence = Enumerable.Range(1, 2);
            
// Fold a sequence into a single value.
var result = sequence
    .Fold((a, b) => a + b);

Console.WriteLine(result);

// This code produces the following output:
// 3
Exceptions
Type Condition
ArgumentNullException

source or folder is null.
InvalidOperationException

source does not contain exactly 2 elements.
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Fold<T, TResult>(IEnumerable<T>, Func<T, T, T, TResult>)

Returns the result of applying a function to a sequence of 3 elements.

Declaration
public static TResult Fold<T, TResult>(this IEnumerable<T> source, Func<T, T, T, TResult> folder)
Parameters
Type Name Description
IEnumerable<T> source

The sequence of items to fold.
Func<T, T, T, TResult> folder

Function to apply to the elements in the sequence.
Returns
Type Description
TResult

The folded value returned by folder.
Type Parameters
Name Description
T

Type of element in the source sequence
TResult

Type of the result
Remarks

This operator uses immediate execution and buffers as many items of the source sequence as necessary.

Examples

The following code example demonstrates how to apply a projection to a sequence of 3 elements using Fold.

var sequence = Enumerable.Range(1, 3);
            
// Fold a sequence into a single value.
var result = sequence
    .Fold((a, b, c) => a + b + c);

Console.WriteLine(result);

// This code produces the following output:
// 6
Exceptions
Type Condition
ArgumentNullException

source or folder is null.
InvalidOperationException

source does not contain exactly 3 elements.
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Fold<T, TResult>(IEnumerable<T>, Func<T, T, T, T, TResult>)

Returns the result of applying a function to a sequence of 4 elements.

Declaration
public static TResult Fold<T, TResult>(this IEnumerable<T> source, Func<T, T, T, T, TResult> folder)
Parameters
Type Name Description
IEnumerable<T> source

The sequence of items to fold.
Func<T, T, T, T, TResult> folder

Function to apply to the elements in the sequence.
Returns
Type Description
TResult

The folded value returned by folder.
Type Parameters
Name Description
T

Type of element in the source sequence
TResult

Type of the result
Remarks

This operator uses immediate execution and buffers as many items of the source sequence as necessary.

Examples

The following code example demonstrates how to apply a projection to a sequence of 4 elements using Fold.

var sequence = Enumerable.Range(1, 4);
            
// Fold a sequence into a single value.
var result = sequence
    .Fold((a, b, c, d) => a + b + c + d);

Console.WriteLine(result);

// This code produces the following output:
// 10
Exceptions
Type Condition
ArgumentNullException

source or folder is null.
InvalidOperationException

source does not contain exactly 4 elements.
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Fold<T, TResult>(IEnumerable<T>, Func<T, T, T, T, T, TResult>)

Returns the result of applying a function to a sequence of 5 elements.

Declaration
public static TResult Fold<T, TResult>(this IEnumerable<T> source, Func<T, T, T, T, T, TResult> folder)
Parameters
Type Name Description
IEnumerable<T> source

The sequence of items to fold.
Func<T, T, T, T, T, TResult> folder

Function to apply to the elements in the sequence.
Returns
Type Description
TResult

The folded value returned by folder.
Type Parameters
Name Description
T

Type of element in the source sequence
TResult

Type of the result
Remarks

This operator uses immediate execution and buffers as many items of the source sequence as necessary.

Examples

The following code example demonstrates how to apply a projection to a sequence of 5 elements using Fold.

var sequence = Enumerable.Range(1, 5);
            
// Fold a sequence into a single value.
var result = sequence
    .Fold((a, b, c, d, e) => a + b + c + d + e);

Console.WriteLine(result);

// This code produces the following output:
// 15
Exceptions
Type Condition
ArgumentNullException

source or folder is null.
InvalidOperationException

source does not contain exactly 5 elements.
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Fold<T, TResult>(IEnumerable<T>, Func<T, T, T, T, T, T, TResult>)

Returns the result of applying a function to a sequence of 6 elements.

Declaration
public static TResult Fold<T, TResult>(this IEnumerable<T> source, Func<T, T, T, T, T, T, TResult> folder)
Parameters
Type Name Description
IEnumerable<T> source

The sequence of items to fold.
Func<T, T, T, T, T, T, TResult> folder

Function to apply to the elements in the sequence.
Returns
Type Description
TResult

The folded value returned by folder.
Type Parameters
Name Description
T

Type of element in the source sequence
TResult

Type of the result
Remarks

This operator uses immediate execution and buffers as many items of the source sequence as necessary.

Examples

The following code example demonstrates how to apply a projection to a sequence of 6 elements using Fold.

var sequence = Enumerable.Range(1, 6);
            
// Fold a sequence into a single value.
var result = sequence
    .Fold((a, b, c, d, e, f) => a + b + c + d + e + f);

Console.WriteLine(result);

// This code produces the following output:
// 21
Exceptions
Type Condition
ArgumentNullException

source or folder is null.
InvalidOperationException

source does not contain exactly 6 elements.
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Fold<T, TResult>(IEnumerable<T>, Func<T, T, T, T, T, T, T, TResult>)

Returns the result of applying a function to a sequence of 7 elements.

Declaration
public static TResult Fold<T, TResult>(this IEnumerable<T> source, Func<T, T, T, T, T, T, T, TResult> folder)
Parameters
Type Name Description
IEnumerable<T> source

The sequence of items to fold.
Func<T, T, T, T, T, T, T, TResult> folder

Function to apply to the elements in the sequence.
Returns
Type Description
TResult

The folded value returned by folder.
Type Parameters
Name Description
T

Type of element in the source sequence
TResult

Type of the result
Remarks

This operator uses immediate execution and buffers as many items of the source sequence as necessary.

Examples

The following code example demonstrates how to apply a projection to a sequence of 7 elements using Fold.

var sequence = Enumerable.Range(1, 7);
            
// Fold a sequence into a single value.
var result = sequence
    .Fold((a, b, c, d, e, f, g) =>
        a + b + c + d + e + f + g);

Console.WriteLine(result);

// This code produces the following output:
// 28
Exceptions
Type Condition
ArgumentNullException

source or folder is null.
InvalidOperationException

source does not contain exactly 7 elements.
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Fold<T, TResult>(IEnumerable<T>, Func<T, T, T, T, T, T, T, T, TResult>)

Returns the result of applying a function to a sequence of 8 elements.

Declaration
public static TResult Fold<T, TResult>(this IEnumerable<T> source, Func<T, T, T, T, T, T, T, T, TResult> folder)
Parameters
Type Name Description
IEnumerable<T> source

The sequence of items to fold.
Func<T, T, T, T, T, T, T, T, TResult> folder

Function to apply to the elements in the sequence.
Returns
Type Description
TResult

The folded value returned by folder.
Type Parameters
Name Description
T

Type of element in the source sequence
TResult

Type of the result
Remarks

This operator uses immediate execution and buffers as many items of the source sequence as necessary.

Examples

The following code example demonstrates how to apply a projection to a sequence of 8 elements using Fold.

var sequence = Enumerable.Range(1, 8);
            
// Fold a sequence into a single value.
var result = sequence
    .Fold((a, b, c, d, e, f, g, h) =>
        a + b + c + d + e + f + g + h);

Console.WriteLine(result);

// This code produces the following output:
// 36
Exceptions
Type Condition
ArgumentNullException

source or folder is null.
InvalidOperationException

source does not contain exactly 8 elements.
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Fold<T, TResult>(IEnumerable<T>, Func<T, T, T, T, T, T, T, T, T, TResult>)

Returns the result of applying a function to a sequence of 9 elements.

Declaration
public static TResult Fold<T, TResult>(this IEnumerable<T> source, Func<T, T, T, T, T, T, T, T, T, TResult> folder)
Parameters
Type Name Description
IEnumerable<T> source

The sequence of items to fold.
Func<T, T, T, T, T, T, T, T, T, TResult> folder

Function to apply to the elements in the sequence.
Returns
Type Description
TResult

The folded value returned by folder.
Type Parameters
Name Description
T

Type of element in the source sequence
TResult

Type of the result
Remarks

This operator uses immediate execution and buffers as many items of the source sequence as necessary.

Examples

The following code example demonstrates how to apply a projection to a sequence of 9 elements using Fold.

var sequence = Enumerable.Range(1, 9);
            
// Fold a sequence into a single value.
var result = sequence
    .Fold((a, b, c, d, e, f, g, h, i) =>
        a + b + c + d + e + f + g + h + i);

Console.WriteLine(result);

// This code produces the following output:
// 45
Exceptions
Type Condition
ArgumentNullException

source or folder is null.
InvalidOperationException

source does not contain exactly 9 elements.
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Fold<T, TResult>(IEnumerable<T>, Func<T, T, T, T, T, T, T, T, T, T, TResult>)

Returns the result of applying a function to a sequence of 10 elements.

Declaration
public static TResult Fold<T, TResult>(this IEnumerable<T> source, Func<T, T, T, T, T, T, T, T, T, T, TResult> folder)
Parameters
Type Name Description
IEnumerable<T> source

The sequence of items to fold.
Func<T, T, T, T, T, T, T, T, T, T, TResult> folder

Function to apply to the elements in the sequence.
Returns
Type Description
TResult

The folded value returned by folder.
Type Parameters
Name Description
T

Type of element in the source sequence
TResult

Type of the result
Remarks

This operator uses immediate execution and buffers as many items of the source sequence as necessary.

Examples

The following code example demonstrates how to apply a projection to a sequence of 10 elements using Fold.

var sequence = Enumerable.Range(1, 10);
            
// Fold a sequence into a single value.
var result = sequence
    .Fold((a, b, c, d, e, f, g, h, i, j) =>
        a + b + c + d + e + f + g + h + i + j);

Console.WriteLine(result);

// This code produces the following output:
// 55
Exceptions
Type Condition
ArgumentNullException

source or folder is null.
InvalidOperationException

source does not contain exactly 10 elements.
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Fold<T, TResult>(IEnumerable<T>, Func<T, T, T, T, T, T, T, T, T, T, T, TResult>)

Returns the result of applying a function to a sequence of 11 elements.

Declaration
public static TResult Fold<T, TResult>(this IEnumerable<T> source, Func<T, T, T, T, T, T, T, T, T, T, T, TResult> folder)
Parameters
Type Name Description
IEnumerable<T> source

The sequence of items to fold.
Func<T, T, T, T, T, T, T, T, T, T, T, TResult> folder

Function to apply to the elements in the sequence.
Returns
Type Description
TResult

The folded value returned by folder.
Type Parameters
Name Description
T

Type of element in the source sequence
TResult

Type of the result
Remarks

This operator uses immediate execution and buffers as many items of the source sequence as necessary.

Examples

The following code example demonstrates how to apply a projection to a sequence of 11 elements using Fold.

var sequence = Enumerable.Range(1, 11);
            
// Fold a sequence into a single value.
var result = sequence
    .Fold((a, b, c, d, e, f, g, h, i, j, k) =>
        a + b + c + d + e + f + g + h + i + j + k);

Console.WriteLine(result);

// This code produces the following output:
// 66
Exceptions
Type Condition
ArgumentNullException

source or folder is null.
InvalidOperationException

source does not contain exactly 11 elements.
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Fold<T, TResult>(IEnumerable<T>, Func<T, T, T, T, T, T, T, T, T, T, T, T, TResult>)

Returns the result of applying a function to a sequence of 12 elements.

Declaration
public static TResult Fold<T, TResult>(this IEnumerable<T> source, Func<T, T, T, T, T, T, T, T, T, T, T, T, TResult> folder)
Parameters
Type Name Description
IEnumerable<T> source

The sequence of items to fold.
Func<T, T, T, T, T, T, T, T, T, T, T, T, TResult> folder

Function to apply to the elements in the sequence.
Returns
Type Description
TResult

The folded value returned by folder.
Type Parameters
Name Description
T

Type of element in the source sequence
TResult

Type of the result
Remarks

This operator uses immediate execution and buffers as many items of the source sequence as necessary.

Examples

The following code example demonstrates how to apply a projection to a sequence of 12 elements using Fold.

var sequence = Enumerable.Range(1, 12);
            
// Fold a sequence into a single value.
var result = sequence
    .Fold((a, b, c, d, e, f, g, h, i, j, k, l) =>
        a + b + c + d + e + f + g + h + i + j + k + l);

Console.WriteLine(result);

// This code produces the following output:
// 78
Exceptions
Type Condition
ArgumentNullException

source or folder is null.
InvalidOperationException

source does not contain exactly 12 elements.
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Fold<T, TResult>(IEnumerable<T>, Func<T, T, T, T, T, T, T, T, T, T, T, T, T, TResult>)

Returns the result of applying a function to a sequence of 13 elements.

Declaration
public static TResult Fold<T, TResult>(this IEnumerable<T> source, Func<T, T, T, T, T, T, T, T, T, T, T, T, T, TResult> folder)
Parameters
Type Name Description
IEnumerable<T> source

The sequence of items to fold.
Func<T, T, T, T, T, T, T, T, T, T, T, T, T, TResult> folder

Function to apply to the elements in the sequence.
Returns
Type Description
TResult

The folded value returned by folder.
Type Parameters
Name Description
T

Type of element in the source sequence
TResult

Type of the result
Remarks

This operator uses immediate execution and buffers as many items of the source sequence as necessary.

Examples

The following code example demonstrates how to apply a projection to a sequence of 13 elements using Fold.

var sequence = Enumerable.Range(1, 13);

// Fold a sequence into a single value.
var result = sequence
    .Fold((a, b, c, d, e, f, g, h, i, j, k, l, m) =>
        a + b + c + d + e + f + g + h + i + j + k + l + m);

Console.WriteLine(result);

// This code produces the following output:
// 91
Exceptions
Type Condition
ArgumentNullException

source or folder is null.
InvalidOperationException

source does not contain exactly 13 elements.
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Fold<T, TResult>(IEnumerable<T>, Func<T, T, T, T, T, T, T, T, T, T, T, T, T, T, TResult>)

Returns the result of applying a function to a sequence of 14 elements.

Declaration
public static TResult Fold<T, TResult>(this IEnumerable<T> source, Func<T, T, T, T, T, T, T, T, T, T, T, T, T, T, TResult> folder)
Parameters
Type Name Description
IEnumerable<T> source

The sequence of items to fold.
Func<T, T, T, T, T, T, T, T, T, T, T, T, T, T, TResult> folder

Function to apply to the elements in the sequence.
Returns
Type Description
TResult

The folded value returned by folder.
Type Parameters
Name Description
T

Type of element in the source sequence
TResult

Type of the result
Remarks

This operator uses immediate execution and buffers as many items of the source sequence as necessary.

Examples

The following code example demonstrates how to apply a projection to a sequence of 14 elements using Fold.

var sequence = Enumerable.Range(1, 14);

// Fold a sequence into a single value.
var result = sequence
    .Fold((a, b, c, d, e, f, g, h, i, j, k, l, m, n) =>
        a + b + c + d + e + f + g + h + i + j + k + l + m + n);

Console.WriteLine(result);

// This code produces the following output:
// 105
Exceptions
Type Condition
ArgumentNullException

source or folder is null.
InvalidOperationException

source does not contain exactly 14 elements.
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Fold<T, TResult>(IEnumerable<T>, Func<T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, TResult>)

Returns the result of applying a function to a sequence of 15 elements.

Declaration
public static TResult Fold<T, TResult>(this IEnumerable<T> source, Func<T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, TResult> folder)
Parameters
Type Name Description
IEnumerable<T> source

The sequence of items to fold.
Func<T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, TResult> folder

Function to apply to the elements in the sequence.
Returns
Type Description
TResult

The folded value returned by folder.
Type Parameters
Name Description
T

Type of element in the source sequence
TResult

Type of the result
Remarks

This operator uses immediate execution and buffers as many items of the source sequence as necessary.

Examples

The following code example demonstrates how to apply a projection to a sequence of 15 elements using Fold.

var sequence = Enumerable.Range(1, 15);

// Fold a sequence into a single value.
var result = sequence
    .Fold((a, b, c, d, e, f, g, h, i, j, k, l, m, n, o) =>
        a + b + c + d + e + f + g + h + i + j + k + l + m + n + o);

Console.WriteLine(result);

// This code produces the following output:
// 120
Exceptions
Type Condition
ArgumentNullException

source or folder is null.
InvalidOperationException

source does not contain exactly 15 elements.
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Fold<T, TResult>(IEnumerable<T>, Func<T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, TResult>)

Returns the result of applying a function to a sequence of 16 elements.

Declaration
public static TResult Fold<T, TResult>(this IEnumerable<T> source, Func<T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, TResult> folder)
Parameters
Type Name Description
IEnumerable<T> source

The sequence of items to fold.
Func<T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, T, TResult> folder

Function to apply to the elements in the sequence.
Returns
Type Description
TResult

The folded value returned by folder.
Type Parameters
Name Description
T

Type of element in the source sequence
TResult

Type of the result
Remarks

This operator uses immediate execution and buffers as many items of the source sequence as necessary.

Examples

The following code example demonstrates how to apply a projection to a sequence of 16 elements using Fold.

var sequence = Enumerable.Range(1, 16);

// Fold a sequence into a single value.
var result = sequence
    .Fold((a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p) =>
        a + b + c + d + e + f + g + h + i + j + k + l + m + n + o + p);

Console.WriteLine(result);

// This code produces the following output:
// 136
Exceptions
Type Condition
ArgumentNullException

source or folder is null.
InvalidOperationException

source does not contain exactly 16 elements.