How do I round numbers in Lua? [Answered] [closed]

Kenetec's answer is different from the standard definition of "rounding."

Generally, round(0.5) is considered to be 1, not 0, but Kenetec's will return 0 because it uses > 0.5 instead of >= 0.5

Nevertheless, the ternary operation that Kenetec's solution performs is needlessly complicated to implement. The following is a true and useful definition of rounding, which is much simpler:

round(x) = floor(x + 0.5)

If we instead write this as

round(x) = x + 0.5 - (x + 0.5) % 1

we get a 20% speedup over Kenetec's solution (if performance is significant).

To round your number, you can make use of the math.floor and math.ceil functions.

math.floor will always round down to the next integer, and math.ceil will always round up. There is no built-in function to round "normally", meaning if the decimal is .5 or greater, we go up, and if it is lower, we go down.

However, not to worry! We can create our own function to do just this.

function round(n)
    return n % 1 >= 0.5 and math.ceil(n) or math.floor(n)
end

This function makes use of the modulus operator, which gives us the remainder of a division operation. Because we are using 1, it will try to divide the number by 1, and then give us the remainder, which will be the decimal that was with the whole number. Then, we compare it to see if it is greater than 0.5, and if it is, we will use the math.ceil function on it to round up, and if not, the math.floor function to round down. This function makes use of Lua's boolean operators to allow us to create this operation in one line, as opposed to using an if statement.