Randomly choose negative or positive while excluding zero

[dreadkillz]

I was thinking of using a while loop:

Code: Select all

local num = math.random(-1,1)
while num == 0 do
 num = math.random(-1,1)
end

Don't seem good code spite of work. So the program will hang in loop till haven't the luck of not be a zero?

Hmm. Good point. It it silly to be stuck in a loop if you don't get what you want, and there's the offchance that you could get consecutive 0's ten times in a row and waste cpu cycles. My example would be something NOT to do then.

[timmeh42]

Code: Select all

local num = math.pow(-1,math.random())

Maybe this? Least hackish, as it doesn't involve any other number than -1, but the math.pow might be slow.

[bartbes]

Let's not forget it doesn't work, seeing as math.random() returns a number between 0 and 1, so you can get fractions. Fixing that however would work.. but it looks pretty damned hackish.

[Nixola]

I'd suggest using "^", I think it's faster

[timmeh42]

Ah damn, i thought it was integers only. (and that was a very silly thing to think, too, considering I was reading straight out of the manual)

Code: Select all

local num = math.pow(-1,math.random(0,1))

That should work, but probably still slower than others.

Also is " ^ " allowed? And if so why should it be faster than math.pow?

[Petunien]

I'm not experienced and at the beginning, though, but for me bartbes' solution looks as fastest as can be.

One line and on every call it returns -1 or 1, nothing other.

Or?

[coffee]

I'm not experienced and at the beginning, though, but for me bartbes' solution looks as fastest as can be.

One line and on every call it returns -1 or 1, nothing other.

Or?

Could be. However boolsheet consider that his method could be faster than bartbes/robin one. I as hobby coder can't tell wich one is executed first including yours. Just to add that speed isn't all. Jasoco was worried about the "hack" factor. I too also consider that sometimes loose a bit of speed for clean code readability isn't really a loss. However major both points is the ideal.

[Nixola]

"^" is not allowed, just checked... Why do I remember that I used it then?
EDIT: Lua doesn't accept it, LÖVE does

[Boolsheet]

"^" is not allowed, just checked... Why do I remember that I used it then?
EDIT: Lua doesn't accept it, LÖVE does

LÖVE does not modify Lua in any way and exponention with ^ is in Lua's reference manual since at least version 2.1. There must be an error in your test or you are looking for something else.

And if so why should it be faster than math.pow?

^ is faster because math.pow involves a table lookup and a function call.

[timmeh42]

^ is faster because math.pow involves a table lookup and a function call.

And " ^ " isn't just a reference call to math.pow? And if not, why does math.pow use a slow method, when lua is supposedly a fast language?