List.scan<'T,'State> Function (F#)

Article
07/11/2012

Applies a function to each element of the collection, threading an accumulator argument through the computation. This function takes the second argument, and applies the function to it and the first element of the list. Then, it passes this result into the function along with the second element, and so on. Finally, it returns the list of intermediate results and the final result.

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

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

// Signature:
List.scan : ('State -> 'T -> 'State) -> 'State -> 'T list -> 'State list

// Usage:
List.scan folder state list

Parameters

folder
Type: 'State -> 'T -> 'State

The function to update the state given the input elements.
state
Type: 'State

The initial state.
list
Type: 'Tlist

The input list.

Return Value

The list of states.

Remarks

This function is named Scan 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 shows how to use List.scan.

let initialBalance = 1122.73
let transactions = [ -100.00; +450.34; -62.34; -127.00; -13.50; -12.92 ]
let balances =
    List.scan (fun balance transactionAmount -> balance + transactionAmount)
              initialBalance transactions
printfn "Initial balance:\n $%10.2f" initialBalance
printfn "Transaction   Balance" 
for i in 0 .. List.length transactions - 1 do
    printfn "$%10.2f $%10.2f" transactions.[i] balances.[i]
printfn "Final balance:\n $%10.2f" balances.[ List.length balances - 1]

Output

Initial balance:
 $   1122.73
Transaction   Balance
$   -100.00 $   1122.73
$    450.34 $   1022.73
$    -62.34 $   1473.07
$   -127.00 $   1410.73
$    -13.50 $   1283.73
$    -12.92 $   1270.23
Final balance:
 $   1257.31

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