R/check_element.R

In yufree/xMSannotator: xMSannotator: R package for network based annotation of metabolomics data.

check_element <- function(curformula, elementname) {
    
    curformula <- as.character(curformula)
    strsplit_var <- strsplit(curformula, split = "")
    
    strsplit_elem <- strsplit(elementname, split = "")
    elem_len <- length(strsplit_elem[[1]])
    
    g3 <- gregexpr(curformula, pattern = paste(elementname, 
        "[0-9]*", sep = ""))
    
    numelement <- 0
    
    if (length(g3) > 0) {
        if (elem_len > 1) {
            
            regexp_len3 <- attr(g3[[1]], "match.length")[1]
            if (regexp_len3 > 2) {
                regexp_len3 <- attr(g3[[1]], "match.length")[1] - 
                  elem_len + 1
            } else {
                regexp_len3 <- attr(g3[[1]], "match.length")[1] - 
                  elem_len
            }
        } else {
            regexp_len3 <- attr(g3[[1]], "match.length")[1] - 
                elem_len
        }
        
        if (regexp_len3 >= 0) {
            
            if (regexp_len3 == 0) {
                numelement <- 1
                
            } else {
                numelement <- paste(strsplit_var[[1]][(g3[[1]][1] + 
                  elem_len):(g3[[1]][1] + regexp_len3)], 
                  collapse = "")
                
                numelement <- as.numeric(numelement)
                
            }
        } else {
            numelement <- 0
            
        }
        
    }
    return(numelement)
}