Randomly choose negative or positive while excluding zero

[Jasoco]

Anyone have a better easier way to randomly choose between -1 and 1 (Positive and negative) than what I've come up with so far?

One way of doing it

Code: Select all

local num = math.random(0,1)
if num == 0 then num = -1 end

One I just came up with

Code: Select all

local neg = { -1, 1 }
num = neg[math.random(1,2)]

Surely there's a different way, or is this the best way?

[Boolsheet]

There's also:

Code: Select all

num = math.random() >= 0.5 and 1 or -1

They all perform about the same.

What do you mean by 'the best way'? Best way to do what?

[Jasoco]

I dunno. Most efficient and least "hacky". There's always someone who will say "You're coding the silly way" when looking at another person's code.

[bartbes]

I used to do stuff like math.random(0, 1)*2-1.

[Robin]

I used to do stuff like math.random(0, 1)*2-1.

Yeah, I'd do that too.

[Boolsheet]

"You're coding the silly way"

The only way to enjoy the quirks of programming languages.
In this case, the winner is probably what's most readable to you.

Using a table uses up some memory and it has an average speed.
If you want speed, then something like this wins (not by much):

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local c
if math.random() >= 0.5 then -- Instead of math.random there would be a local variable pointing to the function.
    c = 1
else
    c = -1
end

Specifying a range for math.random makes Lua do more work and 'if .. then .. end' is faster than the ternary-style '... and ... or ...'.

[coffee]

Well, without doubt bartbes and Robin's way is much more clever, short and faster. But I end to prefer a more long, "legible" as the second method from Jasoco. Don't know, feels like the correct cleaner (but not the efficient coder) way to do.

Code: Select all

rnd = choose({-1,1})
function choose(t)
    return t[math.random(1,2)]
end

EDITED:
Thank you Jasoco, at the end I made a handy table random element selector.

Code: Select all

function choose(t)
    if t[1] then return t[math.random(1,#t)]
end

[Boolsheet]

faster

Faster to write maybe, but not faster in execution.

[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

[coffee]

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?