I would like to replace some numbers in the text column of my data. The numbers are either 8 or 9 digits and in two formats.  This is snapshot of the data:
df <- data.frame(
  notes = c(
    'my number is 123-41-567',
    "321 12 788 is valid",
    'why not taking 987-012-678',
    '120 967 325 is correct'
  )
)
df %>% select(notes)
                       notes
1    my number is 123-41-567
2        321 12 788 is valid
3 why not taking 987-012-678
4     120 967 325 is correct
I need to replace them all with a term such as aaaaa. Hence, the data should look like:
           notes
1     my number is aaaaa
2        aaaaa is valid
3   why not taking aaaaa
4     aaaaa is correct
Thank you in advance!
 
     
    