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”:
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Create a list of integers starting with 5 and incrementing by 2 each time that correspond to the letters "a" to "j":
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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:
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The function works on expressions that are not lists :
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Because the length of an Association is equal to its number of key value pairs, the function can be sensibly applied to associations:
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The function looks only at the first level of an expression to determine the correspondence :
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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:
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Use CorrespondingIntegers to develop indices into a training and test set used for machine learning:
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Index the terms in some document both backward and forward:
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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:
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