readr::parse_number with leading zero

I would like to parse numbers that have a leading zero.

I tried readr::parse_number, however, it omits the leading zero.

library(readr)

parse_number("thankyouverymuch02")
#> [1] 2

^{Created on 2022-12-30 with reprex v2.0.2}

The desired output would be 02

Solution

The simplest and most naive would be:

gsub("\\D", "", "thankyouverymuch02")
[1] "02"

The regex special "\\d" matches a single 0-9 character only; the inverse is "\\D" which matches a single character that is anything except 0-9.

If you have strings with multiple patches of numbers and you want them to be distinct, neither parse_number nor this simple gsub is going to work.

gsub("\\D", "", vec)
# [1] "02"   "0302"

For that, it must always return a list (since we don't necessarily know a priori how may elements have 0, 1 or more number-groups).

vec <- c("thankyouverymuch02", "thank03youverymuch02")
regmatches(vec, gregexpr("\\d+", vec))
# [[1]]
# [1] "02"
# [[2]]
# [1] "03" "02"

#### equivalently
stringr::str_extract_all(vec, "\\d+")
# [[1]]
# [1] "02"
# [[2]]
# [1] "03" "02"