Processing each item in a list of lists of items and re-nesting in Nextflow

listOfListsOfItems.nf

#!/usr/bin/env nextflow

itemLists = [ [1, 2, 3, 4], [5, 6, 7], [8] ]

def groupIdx = 0
itemListChannel = 
	Channel
		.from(itemLists)
		.flatMap { it -> L:{ groupIdx++; it.collect { [ groupIdx, it ] } } }

process itemProcess {
	input:
	val item from itemListChannel
	
	output:
	val item into itemChannel
	
	exec:
	println("Performing itemProcess on ${item}")
}

itemChannel
	.groupTuple(by: 0)
	.flatMap { it -> [ it[1] ] }
	.subscribe { println("receiving ${it}") }

listOfListsOfItemsOrderPreserving.nf

#!/usr/bin/env nextflow

itemLists = [ [1, 2, 3, 4], [5, 6, 7], [8] ]

def groupIdx = 0
itemListChannel = 
	Channel
		.from(itemLists)
		.flatMap { it -> groupIdx++; itemIdx = 0; it.collect { [ groupIdx, ++itemIdx, it ] } }

process itemProcess {

	input:
	val item from itemListChannel
	
	output:
	val result into itemChannel
	
	exec:
	println("Performing itemProcess on ${item}")
	key = item[0]
	order = item[1]
	value = item[2]
	result = [key, [ order, value * 2] ]
}

itemChannel
	.groupTuple(by: 0)
	.flatMap { it2 -> [ it2[1].sort { it[0] }.collect { it[1] } ] }
	.subscribe { println("receiving ${it}") }