[R] Best way to test for numeric digits?

[Rui Barradas]

Às 15:59 de 18/10/2023, Leonard Mada via R-help escreveu:
> 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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Hello,

If you want to extract chemical elements symbols, the following might work.
It uses the periodic table in GitHub package chemr and a package stringr 
function.


devtools::install_github("paleolimbot/chemr")



split_chem_elements <- function(x) {
   data(pt, package = "chemr", envir = environment())
   el <- pt$symbol[order(nchar(pt$symbol), decreasing = TRUE)]
   pat <- paste(el, collapse = "|")
   stringr::str_extract_all(x, pat)
}

mol <- c("CCl3F", "Li4Al4H16", "CCl2CO2AlPO4SiO4Cl")
split_chem_elements(mol)
#> [[1]]
#> [1] "C"  "Cl" "F"
#>
#> [[2]]
#> [1] "Li" "Al" "H"
#>
#> [[3]]
#>  [1] "C"  "Cl" "C"  "O"  "Al" "P"  "O"  "Si" "O"  "Cl"


It is also possible to rewrite the function without calls to non base 
packages but that will take some more work.

Hope this helps,

Rui Barradas


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