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 -> ^UA function that transforms the list elements into the type to be summed.
list
Type: 'T listThe 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 7, Windows Vista SP2, Windows XP SP3, Windows XP x64 SP2, Windows Server 2008 R2, Windows Server 2008 SP2, Windows Server 2003 SP2
Version Information
F# Runtime
Supported in: 2.0, 4.0
Silverlight
Supported in: 3