Parsing date in Mon, DD, YYYY format using RegEx in R

Question

I am attempting to parse a date from a string of text. I'm assuming the best way to do this is regex, but I haven't quite found a solution that works.

First, I used a CSS selector to grab a date from a website.

date <-html_nodes(x=doc, css=".middleheadline+ .topnewsbar b") %>% html_text()

This produces:

[1] "\r\n        Washington,\r\n        Jan 5, 2011"

I want to extract the date itself (here, Jan 5, 2011) from this string. NOTE: the month can be any month, the date can be any date, and the year can be anything from 2011-2015, so I'm trying to find an expression that can generally parse a date in the Mon D[D], YYYY format.

Here's one attempt:

date <-str_extract_all(string=date, pattern='[A-Z][a-z]{3,4} ([0-9]{1,2}), [0-9]{4}')

This produces character(0)

And another:

grep("[A-Z][a-z]{3,4} ([0-9]{1,2}), [0-9]{4}", date, value=TRUE)

which also produces character(0)

Any tips?

Answer 1

You may also try strsplit(). Sometimes I prefer it over a mind-numbing regular expression.

test <- c("\r\n        Washington,\r\n        Jan 5, 2011",
    "\r\n        Boston,\r\n        Mar 15, 2015")

vapply(strsplit(test, ".*\n\\s+"), "[", "", 2)
# [1] "Jan 5, 2011"  "Mar 15, 2015"

as.Date(vapply(strsplit(test, ".*\n\\s+"), "[", "", 2), "%b %d, %Y")
# [1] "2011-01-05" "2015-03-15"

Answer 2

You could try this:

date <-str_extract_all(string=date, pattern='\\w+\\s\\d+(st)?(nd)?(rd)?(th)?,\\s+\\d+')

HERE test link.

Answer 3

A function to convert the dates:

make_dates <- function(x, date_format=TRUE, split="\n") {
  dates <- lapply(strsplit(x, split), function(x) {
    grep("\\w+ \\d+, \\d+", x, value=T)})

  if(date_format) {
    strptime(gsub("\\s", "", dates), format="%b%d,%Y")
  } else { gsub(".*?(\\w.*)", "\\1", dates)}
}

test <- c("\r\n        Washington,\r\n        Jan 5, 2011",
       "\r\n        Boston,\r\n        Mar 15, 2015")

make_dates(test)
#[1] "2011-01-05 EST" "2015-03-15 EDT"
make_dates(test, FALSE)
#[1] "Jan 5, 2011"  "Mar 15, 2015"