Rounding Number Based on Significant Figures

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#1

If I have a number and want to round it either up or down according to significant figures how would I go about doing so?

Example: I want to round a series of numbers to two sig figs.
1: 56,218,489 → 56,000,000
2: 7,380 → 7,400
3: 918,247,543 → 92,000,000

Any help or a push in the right direction would be gratefully appreciated!

#2

You could use the %.[n]g or %.[n]e specifier in string.format but it does convert them to scientific notation for some values (you should be able to convert them into decimal form using string manipulation).

#4

Here’s an implementation that handles signed integers.

local function RoundToSignificantFigures(Number, SignificantFigures)
	Number = math.round(Number) --Integer coercion.
	local Divisor = if Number < 0 then string.len(Number) - SignificantFigures - 1 else string.len(Number) - SignificantFigures
	return math.round(Number / math.pow(10, Divisor)) * math.pow(10, Divisor)
end

local Values = {56218489, 7380, 918247543}
for _, Value in ipairs(Values) do
	print(RoundToSignificantFigures(Value, 2))
end

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