Extracting numbers from vectors of strings

Question

I have string like this:

years<-c("20 years old", "1 years old")

I would like to grep only the numeric number from this vector. Expected output is a vector:

c(20, 1)

How do I go about doing this?

Answer 1

A stringr pipelined solution:

library(stringr)
years %>% str_match_all("[0-9]+") %>% unlist %>% as.numeric

Answer 2

Update Since extract_numeric is deprecated, we can use parse_number from readr package.

library(readr)
parse_number(years)

Here is another option with extract_numeric

library(tidyr)
extract_numeric(years)
#[1] 20  1

Answer 3

I think that substitution is an indirect way of getting to the solution. If you want to retrieve all the numbers, I recommend gregexpr:

matches <- regmatches(years, gregexpr("[[:digit:]]+", years))
as.numeric(unlist(matches))

If you have multiple matches in a string, this will get all of them. If you're only interested in the first match, use regexpr instead of gregexpr and you can skip the unlist.