List.sumBy<'T,^U> Function (F#)

Returns the sum of the results generated by applying the function to each element of the list.

Namespace/Module Path: Microsoft.FSharp.Collections.List

Assembly: FSharp.Core (in FSharp.Core.dll)

// Signature:
List.sumBy : ('T -> ^U) -> 'T list -> ^U (requires ^U with static member (+) and ^U with static member Zero)

// Usage:
List.sumBy projection list

Parameters

• projection
  Type: 'T -> ^U

  A function that transforms the list elements into the type to be summed.

• list
  Type: 'Tlist

  The input list.

Return Value

The resulting sum.

Remarks

This function is named SumBy in compiled assemblies. If you are accessing the function from a .NET language other than F#, or through reflection, use this name.

Example

The following code example illustrates the use of List.sum, List.sumBy, and List.average.

// Compute the sum of the first 10 integers by using List.sum. 
let sum1 = List.sum [1 .. 10]

// Compute the sum of the squares of the elements of a list by using List.sumBy. 
let sum2 = List.sumBy (fun elem -> elem*elem) [1 .. 10]

// Compute the average of the elements of a list by using List.average. 
let avg1 = List.average [0.0; 1.0; 1.0; 2.0]

printfn "%f" avg1

Output

1.000000

Platforms

Windows 8, Windows 7, Windows Server 2012, Windows Server 2008 R2

Version Information

F# Core Library Versions

Supported in: 2.0, 4.0, Portable

See Also

Reference

Collections.List Module (F#)

Microsoft.FSharp.Collections Namespace (F#)