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

Den Delimarsky|Last Updated: 8/18/2017
2 Contributors

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

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

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


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

// Usage:
Seq.sumBy projection source


projection Type: 'T -> ^U

A function to transform items from the input sequence into the quantity that will be summed.

source Type: seq<'T>

The input sequence.

Return Value

The sum of the results of applying the projection function to each element of the sequence.


May throw an OverflowException due to arithmetic overflows.


The results are summed using the checked + operator and Zero property associated with the summed type.

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


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

Collections.Seq Module (F#)

Microsoft.FSharp.Collections Namespace (F#)

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