WorkingDays.pq

/*

Copyright 2020 - 2020 getkks, getkks@live.in

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relinquishment in perpetuity of all present and future rights to this
software under copyright law.

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Project			: Power Query Library @ d:\Development\M\Power-Query

File			: WorkingDays.pq @ d:\Development\M\Power-Query\WorkingDays.pq
File Created	: Saturday, 9th May 2020 3:20:38 pm

Author			: getkks (getkks@live.in)

Change History:

*/
(start as date,
	end as date,
	optional HolidaysList as list) as number =>

let
	LstOfHolidays = if HolidaysList = null then {} else HolidaysList,
	NumLstOfHolidays = List.Transform(LstOfHolidays ,each Number.From(_)),
	LstOfDays = if start<end then {Number.From(start)..Number.From(end)} else {Number.From(end)..Number.From(start)},
	LstDiff  = List.Difference(LstOfDays, NumLstOfHolidays),
	LstMod = List.Transform(LstDiff, each Number.Mod(_, 7)),
	LstSel = List.Select(LstMod, each _>1) ,
	Result = if start<end then List.Count(LstSel)-1 else if start=end then 0 else List.Count(LstSel)*(-1)+1
in
	Result