Cleaning a Data Frame Using Regexp in R

Question

 NUMERO_APPEL
1          NNA
2     VQ-40989
3        41993
4        41993
5        42597
6     VQ-42597
7         DER8
8   40001-2010

I would like to extract the 5 consecutive digits of the strings that have the following format and only the following format, all other strings will be replaced by NAs.

AO-11111
VQ-11111
11111

Answer 1

The simplest way:

library(dplyr)
library(stringi)

df %>%
  mutate(NUMERO_APPEL.fix = 
           NUMERO_APPEL %>% 
             stri_extract_first_regex("[0-9]{5}") %>%
             as.numeric)