fix for digits="pdf" last error digits 950-999 case

[alusiani]

Hi,

the CRAN present version of the package formats with digits="pdg"

1.234 +- 0.0950  ->  1.2 +- 0.1 (expected: 1.23 +- 0.10)

In short, the case of last three digits 950-999 should format to 10 with 2 digits, and formats 1 digit instead.

I have produced here a working version: https://github.com/alusiani-forked/errors, starting from the current https://github.com/cran/errors .

If acceptable, I can propose a pull request. There are some modifications to print.R and utils.R. I have added an additional argument, that could facilitate a future extension to asking the PDG number of digits plus an extra offset. This argument does nothing now.

Cheers,

Alberto

[Enchufa2]

PR welcome. Adding @davidchall to the conversation because he added this functionality. It would be nice to have new tests that fail under the current version and succeed with the fix.

[davidchall]

Hi @Enchufa2 - Yes, @alusiani is correct and this was an oversight on my part in #59.

Below I've highlighted the relevant piece of the PDG guidelines:

5.3. Rounding : While the results shown in the Particle Listings are usually exactly those published by the experiments, the numbers that appear in the Summary Tables (means, averages and limits) are subject to a set of rounding rules.

The basic rule states that if the three highest order digits of the error lie between 100 and 354, we round to two significant digits. If they lie between 355 and 949, we round to one significant digit. Finally, if they lie between 950 and 999, we round up to 1000 and keep two significant digits. In all cases, the central value is given with a precision that matches that of the error. So, for example, the result (coming from an average) 0.827 ± 0.119 would appear as 0.83 ± 0.12, while 0.827 ± 0.367 would turn into 0.8 ± 0.4.

The following test case should be updated such that the final expected value is c("0.8", "1.0"):

errors/tests/testthat/test-print.R

Lines 48 to 51 in 7ed6c27

	x <- set_errors(rep(0.827, 3), c(0.119, 0.367, 0.962))
	expect_equal(format(x, notation="plus-minus", digits="pdg"), sapply(list(
	c("0.83", "0.12"), c("0.8", "0.4"), c("1", "1")),
	paste, collapse=paste("", .pm, "")))