Significant Digits and Rounding Issue

General
1

Why does significant digits function and round function round down in these examples? Result should be 211, but R outputs 210.

signif(x = 210.5, digits = 3)
[1] 210

round(210.5, digits = 0)
[1] 210
2

I think this is due to a behavior of R rounding to nearest even.

See ?round help page

Note that for rounding off a 5, the IEC 60559 standard (see also ‘IEEE 754’) is expected to be used, ‘ go to the even digit ’. Therefore round(0.5) is 0 and round(-1.5) is -2 . However, this is dependent on OS services and on representation error (since e.g. 0.15 is not represented exactly, the rounding rule applies to the represented number and not to the printed number, and so round(0.15, 1) could be either 0.1 or 0.2 ).

3

can you suggest how to solve this issue, so the output rounds to the appropriate number?

4

ceiling() should do the job.

ceiling(210.5)
#> [1] 211

Created on 2020-04-22 by the reprex package (v0.3.0)

5

There is a lot of SO questions on this topic, you could see the inspiration for workaround there:

There is also this blog post and a solution inspired by one on SO

Hope it helps.

6

I think you'll find the term "appropriate number" is arbitrarily defined. And a very good case can be made that always rounding up in the case of a 0.5 is not the best approach to rounding.

You'll find that all respectable programs use this same round-to-even standard. I would recommend embracing it.

7

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