Wolfram Function Repository

Instant-use add-on functions for the Wolfram Language

Function Repository Resource:

 BisectList

Source Notebook

Make a pair of lists consisting of alternate terms from the original list

Contributed by: George Beck

ResourceFunction["BisectList"][{a1,a2,a3,a4,a5,a6,…}]

makes the list {{a1,a3,a5…},{a2,a4,a6,…}}.

Details and Options

ResourceFunction["BisectList"] is a partial inverse function of Riffle.
The two sublists have equal lengths.
If the input list has an odd number of terms, the last term is ignored.
The argument can be an expression other than a list.

Examples

Basic Examples (3) 

The lists being riffled have the same length:

In[1]:=
Riffle[{1, 2, 3}, 100 {1, 2, 3}]
Out[1]=
Image

BisectList gives back the sublists:

In[2]:=
ResourceFunction["BisectList"]@%
Out[2]=
Image

Here, the riffled lists have different lengths:

In[3]:=
Riffle[{1, 2, 3, 4}, 100 {1, 2, 3}]
Out[3]=
Image

BisectList ignores the last term:

In[4]:=
ResourceFunction["BisectList"]@%
Out[4]=
Image

Here the head of the expression is not List:

In[5]:=
ResourceFunction["BisectList"][fgh /@ Range[7]]
Out[5]=
Image

Scope (3) 

Add consecutive pairs of a list:

In[6]:=
Total@ResourceFunction["BisectList"]@Range[20]
Out[6]=
Image

Apply BisectList twice:

In[7]:=
ResourceFunction["BisectList"] /@ ResourceFunction["BisectList"]@Range[32]
Out[7]=
Image

Pull out the interleaved subsequences, making them both positive:

In[8]:=
(-1)^Range[20] RandomInteger[{1, 9}, 20]
Out[8]=
Image
In[9]:=
{-1, 1} ResourceFunction["BisectList"][%]
Out[9]=
Image

Publisher

George Beck

Requirements

Wolfram Language 11.3 (March 2018) or above

Version History

  • 1.0.0 – 01 February 2019

License Information