From f06bda97851046481ecf67a479f2bb9dab5212ef Mon Sep 17 00:00:00 2001
From: Lars Mueller <appgurulars@gmx.de>
Date: Sat, 13 Nov 2021 17:58:40 +0100
Subject: [PATCH] Add iterator aggregation functions

---
 func.lua | 60 ++++++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 58 insertions(+), 2 deletions(-)

diff --git a/func.lua b/func.lua
index 5128ae3..11405a9 100644
--- a/func.lua
+++ b/func.lua
@@ -1,6 +1,6 @@
 -- Localize globals
-local error, coroutine, modlib, unpack
-	= error, coroutine, modlib, unpack
+local error, coroutine, math, modlib, unpack
+	= error, coroutine, math, modlib, unpack
 
 -- Set environment
 local _ENV = {}
@@ -78,6 +78,62 @@ function aggregate(binary_func, total, ...)
 	return total
 end
 
+--+ For all functions which aggregate over single values, use modlib.table.ivalues - not ipairs - for lists!
+--+ Otherwise they will be applied to the indices.
+iterator = {}
+
+function iterator.aggregate(binary_func, total, ...)
+	for value in ... do
+		total = binary_func(total, value)
+	end
+	return total
+end
+
+function iterator.min(less_than_func, ...)
+	local min
+	for value in ... do
+		if min == nil or less_than_func(value, min) then
+			min = value
+		end
+	end
+	return min
+end
+
+function iterator.count(...)
+	local count = 0
+	for _ in ... do
+		count = count + 1
+	end
+	return count
+end
+
+function iterator.sum(...)
+	return iterator.aggregate(add, ...)
+end
+
+function iterator.average(...)
+	local count = 0
+	local sum = 0
+	for value in ... do
+		count = count + 1
+		sum = sum + value
+	end
+	return sum / count
+end
+
+--: ... **restartable** iterator
+-- While a single pass method for calculating the standard deviation exists, it is highly inaccurate
+function iterator.standard_deviation(...)
+	local avg = iterator.average(...)
+	local count = 0
+	local sum = 0
+	for value in ... do
+		count = count + 1
+		sum = sum + (value - avg)^2
+	end
+	return math.sqrt(sum / count)
+end
+
 function override_chain(func, override)
 	return function(...)
 		func(...)