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Hello there,

Is anyone able to tell me why my little bit of code just returns:

[NIL]
[NIL]
[NIL]
[NIL]
...and so on?

I thought maybe I had to manually return something from the function, but I understand all values are global unless declared local - is that right? I thought maybe forcing it into a string with TOSTR might work, but no.

I'm not sure where to go from here.

function _init()
    createtable()
end

function _update()
    pickrandomteam()
end

function _draw()
    print(randteam)
end

-- user functions

function createtable()
    team={"liverpool","welling utd","arsenal","accrington stanley"}
end

function pickrandomteam()
    n=rnd(3)
    randteam=team[n]
end
P#57015 2018-09-23 05:09 ( Edited 2018-09-29 07:02)

D'oh!

Just found the answer - I'm assuming the random number generator produce decimals unless you FLR it.

FLR(RND(3))

P#57016 2018-09-23 05:18 ( Edited 2018-09-23 09:18)
:: Davbo

Hi Pico Noob! You are correct about needing to use flr, however lua arrays are one indexed and rnd gets a number from 0 so you actually need
flr(rnd(3))+1
On top of that, there is a # key in lua that gets the number of items in a table, so you could use
flr(rnd (#team))+1
So then you could add and take away entries from team and this line of code would scale to compensate.

P#57017 2018-09-23 07:56 ( Edited 2018-09-23 11:56)
:: Felice

In fact, it's often useful to have a little function that does exactly that, all in one place:

function trnd(t)
  return t[flr(rnd(#t))+1]
end

color=trnd(palette)
player=trnd(team)
page=trnd(book)
etc.
P#57019 2018-09-23 17:05 ( Edited 2018-09-23 21:05)
:: pom

Note that since array indices usually start at 1, picking a random item can be made a bit simpler by using ceil instead of flr, like so:

function randomitem(xs)
 return xs[ceil(rnd(#xs))]
end
P#57032 2018-09-24 11:22 ( Edited 2018-09-24 15:22)
:: Davbo

As @Felice has pointed out to me before, while it looks like you're saving a token you have to remember that rnd(1) would return between 0 and 0.99999 (or some decimal around there). So doing this method leaves the (very very slim) chance of rnd returning 0, then ceil 0 returns 0 and trying to access element at index 0 causing a nil return.

P#57035 2018-09-24 12:05 ( Edited 2018-09-24 16:07)
:: dw817

If you're not worried about space, here is a robust random function I use in all my code that needs a random operator. It can be used three ways:

a=fnr(nn)

Gives you a random number zero to nn minus one.
a=fnr(8) : 0..1..2..3..4..5..6..7

a=fnr(n1,n2)

Gives you a random number from n1 to n2.
a=fnr(2,6) : 2..3..4..5..6

Reversing numbers also gets you the same results.
a=fnr(6,2) : 2..3..4..5..6

Negative numbers are also allowed.
a=fnr(-3,3) : -3..-2..-1..0..1..2..3

If you're curious about that a=b,b=a that idea comes from Felice. A good way to swap variables without using a 3rd.

As the results are always integer, you don't need to worry about floating point numbers, the decimal place, or returning non-integer values for integer arrays.

-- get random # ---------------
function fnr(a,b)
  if (b==nil) return flr(rnd(a))
  if (a>b) a,b=b,a
  return a+flr(rnd(b-a+1))
end--fnrr(..)
P#57036 2018-09-24 12:28 ( Edited 2018-09-24 16:33)
:: pom

Davbo: good point about ceil(0)!

P#57045 2018-09-24 13:34 ( Edited 2018-09-24 17:34)

Thanks, folks. Helpful stuff.

P#57245 2018-09-29 03:02 ( Edited 2018-09-29 07:02)

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