Question

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ruby floating point errors

In Ruby, when subtracting 4.7 from 5.0, I would expect a result of 0.3 but get:

~ $ irb
1.9.2p290 :001 > 5.0 - 4.7
 => 0.2999999999999998 

I’m guessing there is a reason for this rather than it being a bug? Using BigDecimal objects yields the same result. Is my only option to use round on the result?

Answer 1

Floats lose precision. Nothing can be done about that. So, use:

(5.0 - 4.7).round(1)

and if you had needed more precision:

(0.50 - 0.47).round(2)