Wolfram Function Repository
Instantuse addon functions for the Wolfram Language
Function Repository Resource:
Create a list of positive integers containing as many elements as the expression to which it is applied
ResourceFunction["CorrespondingIntegers"][expr] gives a list {1…n} of positive integers where n is the length of expr. 

ResourceFunction["CorrespondingIntegers"][expr,start,jump] gives a list {start,start+jump,…,start+(n1)×jump} where n is the length of expr. 

ResourceFunction["CorrespondingIntegers"][start,jump] creates an operator that, when applied to an expression expr, gives a list {start,start+jump,…,start+(n1)×jump} where n is the length of expr. 
Create a list of the positive integers corresponding to letters "a" to "j":
In[1]:= 

Out[1]= 

Create a list of integers starting with 5 and incrementing by 2 each time that correspond to the letters "a" to "j":
In[2]:= 

Out[2]= 

Create an operator which, when it an expression, creates a list with the same number of parts as that expression, in which the first element is 1, and in which each successive value is 1 higher:
In[3]:= 

Out[3]= 

The function works on expressions that are not lists :
In[4]:= 

Out[4]= 

Because the length of an Association is equal to its number of key value pairs, the function can be sensibly applied to associations:
In[5]:= 

Out[5]= 

The function looks only at the first level of an expression to determine the correspondence :
In[6]:= 

Out[6]= 

Using non  integer values for the starting value and/or the jump will give a warning, as this is not the purpose for which the function is intended:
In[7]:= 

Out[7]= 

Use CorrespondingIntegers to develop indices into a training and test set used for machine learning:
In[8]:= 

Out[8]= 

Index the terms in some document both backward and forward:
In[9]:= 

Out[9]= 

This function can be combined with Thread to emulate the action of MapIndexed at level 1 where one takes the first part of the index:
In[10]:= 

Out[10]= 

This work is licensed under a Creative Commons Attribution 4.0 International License