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[1]:=
 Out[1]=

### Scope (2)

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

 In[2]:=
 Out[2]=

Make an operator:

 In[3]:=
 Out[3]=

Feed a single list to the operator:

 In[4]:=
 Out[4]=

Feed an initializer and a list to the operator:

 In[5]:=
 Out[5]=

### Applications (3)

Form a continued fraction with increasing power:

 In[6]:=
 Out[6]=

Form a continued fraction with an increasing numerator:

 In[7]:=
 Out[7]=

Form the product :

 In[8]:=
 Out[8]=

SHuisman

## Version History

• 1.0.0 – 20 November 2019