如何从字符串中删除字符并只保留 R 中的数字？

Question

a<- "\n\t\t\t\n\t\t\t\New\n\t\t\t\n\t\t\t\n\t\t\t\t\n\t\t\t\t\t - \n\t\t\t\t\n\t\t\t\t95\n\t\t\t\tdays\n\t\t\t\n\t\t"

How to isolate only the number 95 from this string? I tried the gsub and str_replace but it removes the 95 too I removed this string from a site through the rvest package

Answer 1

We can use gsub from base R to remove all characters that are not digits

gsub("\\D+", "", a)
#[1] "95"

Or as commented by @G Grothendieck

gsub("\\D", "", a)

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Or with str_remove_all

library(stringr)
str_remove_all(a, "\\D+")
#[1] "95"

Answer 2

The previous answers have approached the desired output negatively, by defining patterns for what is to be removed, namely anything that is not a number (hence \\\\D with uppercase D). Here's a positive solution defining what is to be kept, and extracting it via a self-defined function extract :

Define function, including the pattern to be matched \\\\d{2} (ie, two contiguous numbers):

extract <- function(x) unlist(regmatches(x, gregexpr("\\d{2}", x, perl = T)))

Apply function to data a :

extract(a)
[1] "95"

Answer 3

我打算建议使用readr::parse_number但后来我了解到它会在- readr::parse_number失败，然后需要额外的工作，如解释here 。