Function Repository Resource:

# FoldIndexed

Perform a folding operation while also parsing the index as the third argument

Contributed by: Sander Huisman
 ResourceFunction["FoldIndexed"][f,x,{a,b,…}] gives the last element of FoldIndexedList[f,x,{a,b,…}]. ResourceFunction["FoldIndexed"][f,list] is equivalent to ResourceFunction["FoldIndexed"][f,First[list],Rest[list]]. ResourceFunction["FoldIndexed"][f] represents an operator form of ResourceFunction["FoldIndexed"] that can be applied to expressions.

## Details and Options

ResourceFunction["FoldIndexed"][f][list] is equivalent to ResourceFunction["FoldIndexed"][f,list].
ResourceFunction["FoldIndexed"][f][x,list] is equivalent to ResourceFunction["FoldIndexed"][f,x,list].

## Examples

### Basic Examples (1)

Map a function over a list including the index:

 In:= Out= ### Scope (2)

Without an initializer, the first element of list is the initializer:

 In:= Out= Make an operator:

 In:= Out= Feed a single list to the operator:

 In:= Out= Feed an initializer and a list to the operator:

 In:= Out= ### Applications (3)

Form a continued fraction with increasing power:

 In:= Out= Form a continued fraction with an increasing numerator:

 In:= Out= Form the product :

 In:= Out= SHuisman

## Version History

• 1.0.0 – 20 November 2019