Re: Lua Basics: tables as lists?

[William Trenker <wtrenker@...>]

On 8/22/05, Rici Lake <lua@ricilake.net> wrote:
> 
> For loops are not expensive
> 
> > myList = {"a", "b", "cde"}
> > myListString = "|" .. table.concat(myList, "|") .. "|"
> > a = "cde"
> > if string.find(myListString, "|"..a.."|") then
> >     print("found!")
> > else
> >     print("not found")
> > end
> 
> That is very expensive

You're right.  I ran some timed tests over large lists and the for
loop was an order of magnitude faster than concatenating the table
values into a string and doing a string.find.

My intuition was wrong.  I assumed that a for loop was expensive
because it meant running the code in that loop through the interpreter
over and over.  I thought that the single string.find, being done in
C, would be faster.  But, in fact, the time to run the preparatory
table.concat -- for large lists -- is comparitivly very slow  and does
indeed make that approach very expensive.

I'm really beginning to respect the efficiency of the Lua interpreter.

Thanks for the insight,
Bill