Keep a single number from a string, otherwise return NA

keep_number_or_na() extracts digits from each element of a character vector according to the following rules:

• If the string contains exactly one number (one contiguous run of digits), that number is returned (as character). This includes strings made only of digits (e.g. "15") and strings where the number is mixed with letters or other characters (e.g. "ID=15").

• If the string contains no number, the result is NA.

• If the string contains more than one number (e.g. "15;101", "abc12def34"), the result is NA.

The function is vectorised and can be used inside dplyr::mutate().

Usage

keep_number_or_na(x)

Arguments

x

A character vector.

Value

A character vector of the same length as x.

Examples

x <- c("15", "ID=15", "ser", NA, "15;101", "abc12def34")
keep_number_or_na(x)
#> [1] "15" "15" NA   NA   NA   NA  

df <- tibble::tibble(x = x)
dplyr::mutate(df, y = keep_number_or_na(x))
#> # A tibble: 6 × 2
#>   x          y    
#>   <chr>      <chr>
#> 1 15         15   
#> 2 ID=15      15   
#> 3 ser        NA   
#> 4 NA         NA   
#> 5 15;101     NA   
#> 6 abc12def34 NA