[R] Best way to test for numeric digits?

[Ben Bolker]

    There are some answers on Stack Overflow:

https://stackoverflow.com/questions/14984989/how-to-avoid-warning-when-introducing-nas-by-coercion



On 2023-10-18 10:59 a.m., Leonard Mada via R-help wrote:
> Dear List members,
> 
> 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?
> 
> I was working to extract chemical elements from a formula, something 
> like this:
> split.symbol.character = function(x, rm.digits = TRUE) {
>      # Perl is partly broken in R 4.3, but this works:
>      regex = "(?<=[A-Z])(?![a-z]|$)|(?<=.)(?=[A-Z])|(?<=[a-z])(?=[^a-z])";
>      # stringi::stri_split(x, regex = regex);
>      s = strsplit(x, regex, perl = TRUE);
>      if(rm.digits) {
>          s = lapply(s, function(s) {
>              isNotD = is.na(suppressWarnings(as.numeric(s)));
>              s = s[isNotD];
>          });
>      }
>      return(s);
> }
> 
> split.symbol.character(c("CCl3F", "Li4Al4H16", "CCl2CO2AlPO4SiO4Cl"))
> 
> 
> Sincerely,
> 
> 
> Leonard
> 
> 
> Note:
> # works:
> regex = "(?<=[A-Z])(?![a-z]|$)|(?<=.)(?=[A-Z])|(?<=[a-z])(?=[^a-z])";
> strsplit(c("CCl3F", "Li4Al4H16", "CCl2CO2AlPO4SiO4Cl"), regex, perl = T)
> 
> 
> # 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)
> 
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