В Wed, 18 Oct 2023 17:59:01 +0300
Leonard Mada via R-help <r-help@r-project.org> пишет:
> What is the best way to test for numeric digits?
>
> suppressWarnings(as.double(c("Li", "Na", "K", "2", "Rb", "Ca", "3")))
> # [1] NA NA NA 2 NA NA 3
> The above requires the use of the suppressWarnings function. Are
> there any better ways?
This test also has the downside of accepting things like "1.2" and
"+1e-100". Since you need digits only, why not use a regular expression
to test for '^[0-9]+$'?
> I was working to extract chemical elements from a formula, something
> like this:
> split.symbol.character(c("CCl3F", "Li4Al4H16", "CCl2CO2AlPO4SiO4Cl"))
Perhaps the following function could be made to work in your cases?
function(x) regmatches(x, gregexec('([A-Z][a-z]*)([0-9]*)', x))
retval[2,] is the element and retval[3,] is the coefficient. Do you
need brackets? Charges? Non-stoichiometric compounds? (SMILES?)
> # broken in R 4.3.1
> # only slightly "erroneous" with stringi::stri_split
> regex = "(?<=[A-Z])(?![a-z]|$)|(?=[A-Z])|(?<=[a-z])(?=[^a-z])";
> strsplit(c("CCl3F", "Li4Al4H16", "CCl2CO2AlPO4SiO4Cl"), regex, perl =
> T)
strsplit() has special historical behaviour about empty matches:
https://bugs.r-project.org/show_bug.cgi?id=16745
It's unfortunate that it doesn't split on empty matches the way you
would intuitively expect it to, but changing the behaviour at this
point is hard. Even adding a flag may be complicated to implement. Do
you want such a flag?
--
Best regards,
Ivan
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