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. Expe

Answer 1

We can also use str_extract from stringr

years<-c("20 years old", "1 years old")
as.integer(stringr::str_extract(years, "\\d+"))
#[1] 20  1

If there are multiple numbers in the string and we want to extract all of them, we may use str_extract_all which unlike str_extract returns all the macthes.

years<-c("20 years old and 21", "1 years old")
stringr::str_extract(years, "\\d+")
#[1] "20"  "1"

stringr::str_extract_all(years, "\\d+")

#[[1]]
#[1] "20" "21"

#[[2]]
#[1] "1"

Answer 2

You could get rid of all the letters too:

as.numeric(gsub("[[:alpha:]]", "", years))

Likely this is less generalizable though.

Answer 3

After the post from Gabor Grothendieck post at the r-help mailing list

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

library(gsubfn)
pat <- "[-+.e0-9]*\\d"
sapply(years, function(x) strapply(x, pat, as.numeric)[[1]])

Answer 4

A stringr pipelined solution:

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

Answer 5

Extract numbers from any string at beginning position.

x <- gregexpr("^[0-9]+", years)  # Numbers with any number of digits
x2 <- as.numeric(unlist(regmatches(years, x)))

Extract numbers from any string INDEPENDENT of position.

x <- gregexpr("[0-9]+", years)  # Numbers with any number of digits
x2 <- as.numeric(unlist(regmatches(years, x)))