pairs, ipairs and #tablename iteration

iteration.lua

--[[

Tables in Lua may contain both ordered (numbered) and unordered (named) members.  Most of the time, you'll use just named elements, or just numbered elements, but there are surprisingly frequent occasions when it's useful to use both.   You then need to remember if you iterate through members that ...

- #tablename will only go through numbered elements, and will give you nil if there's a gap in the numbering

- pairs will take you through all elements with non-nil values, but won't give you any members which are explicitly or implicitly set to nil

- ipairs will start at the element numbered 1, and go up through numbered elements until it reaches a nil, at which point it will go no further.

source: http://www.wellho.net/resources/ex.php4?item=u105/ph

]]--

print ("Set up a table, indexed, with a hole")
vals = {"one","two","three",nil,"five"}

print ("Iterate through it using #tablename")
for k=1,#vals do
	print (k,vals[k])
end

print ("Add a numbered value after a gap. Works fine")
vals[8] = "eight"
for k=1,#vals do
	print (k,vals[k])
end

print ("Add a named value - but not seen by the loop")
vals["nine"] = "It's 9"
for k=1,#vals do
	print (k,vals[k])
end

print ("Pairs goes through all the elements with values")
for k,v in pairs(vals) do
	print (k,v)
end

print ("Ipairs starts at element 1, goes up 1 at a time and stops when it finds a nil")
for k,v in ipairs(vals) do
	print (k,v)
end