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Check the validity of a CHI number

Source: R/chi_check.R
chi_check.Rd

chi_check takes a CHI number or a vector of CHI numbers with character class. It returns feedback on the validity of the entered CHI number and, if found to be invalid, provides an explanation as to why.

Usage

chi_check(x)

Arguments

x

a CHI number or a vector of CHI numbers with character class.

Value

chi_check returns a character string. Depending on the validity of the entered CHI number, it will return one of the following:

  • Valid CHI

  • Invalid character(s) present

  • Too many characters

  • Too few characters

  • Invalid date

  • Invalid checksum

  • Missing (NA)

  • Missing (Blank)

Details

The Community Health Index (CHI) is a register of all patients in NHS Scotland. A CHI number is a unique, ten-digit identifier assigned to each patient on the index.

The first six digits of a CHI number are a patient's date of birth in DD/MM/YY format.

The ninth digit of a CHI number identifies a patient's sex: odd for male, even for female. The tenth digit is a check digit, denoted checksum.

While a CHI number is made up exclusively of numeric digits, it cannot be stored with numeric class in R. This is because leading zeros in numeric values are silently dropped, a practice not exclusive to R. For this reason, chi_check accepts input values of character class only. A leading zero can be added to a nine-digit CHI number using chi_pad().

chi_check assesses whether an entered CHI number is valid by checking whether the answer to each of the following criteria is Yes:

  • Does it contain no non-numeric characters?

  • Is it ten digits in length?

  • Do the first six digits denote a valid date?

  • Is the checksum digit correct?

Examples

chi_check("0101011237")
#> [1] "Valid CHI"
chi_check(c("0101201234", "3201201234"))
#> [1] "Invalid checksum" "Invalid date"    

library(dplyr)
df <- tibble(chi = c(
  "3213201234",
  "123456789",
  "12345678900",
  "010120123?",
  NA
))
df %>%
  mutate(validity = chi_check(chi))
#> # A tibble: 5 × 2
#>   chi         validity                    
#>   <chr>       <chr>                       
#> 1 3213201234  Invalid date                
#> 2 123456789   Too few characters          
#> 3 12345678900 Too many characters         
#> 4 010120123?  Invalid character(s) present
#> 5 NA          Missing (NA)