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From: "digi_cs" <cosmogen@gmail.com>
Subject: HID:LIST - list arrays
Newsgroups: comp.lang.awk
Date: Thu, 17 Oct 2024 08:20:31 +0300
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Hello!

FYI

	@include “github.com/digics/UID10/uid.lib”	

	LIST = hid::get( “LIST” )


An array (A) in AWK can represent a list of unique items with an undefined order.
To introduce the concept of an array with a defined sequence of its indexes (items),
we need to specify this sequence in a subarray A[LIST] as a simple list:

The element A[ LIST ][ "" ] stores the index of the first item in the list:
	
	# items of A: first, next and last:

	A[ “LIST” ][ “” ] = “first”
                 [ “first” ] = “next”
           	     [ “next” ] = “last”
           	     [ “last” [ = “”
	 [ “first” ]...
	 [ “next” ]...
	 [ “last” ]...

Thus, instead of a for-in loop for array A, we use: 

	i = “”
	while ( “” != i = A[ LIST][ i ] )

		# process A[ i ]

or

	for ( i = “”; “” != i = A[ LIST ][ i ]; ) 

		# process A[ i ]

At the same time, we can still work with the main array in a for-in loop — with one caveat: 

	for ( i in A )
	
		if ( i in HID )

			continue		# this is hid (LIST)

		else

			# process A[ i ]

In case a bidirectional list is needed, another subarray A[LIST][LIST] is created
within the subarray A[LIST], where the items are listed in reverse order,
 and the element A[LIST][LIST][""] stores the index of the last item in the list. 

best regards)


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