Temporarily change locale settings

Question

Actual question

How can I temporarily change/specify the locale settings to be used for certain function calls (e.g. strptime())?

Background

I just ran the following rvest demo:

demo("tripadvisor", package = "rvest")

When it comes to the part where the dates are to be scraped, I run into some problems that most likely are caused by my locale settings: the dates are in an US american format while I'm on a German locale:

require("rvest")
url <- "http://www.tripadvisor.com/Hotel_Review-g37209-d1762915-Reviews-JW_Marriott_Indianapolis-Indianapolis_Indiana.html"

reviews <- url %>%
  html() %>%
  html_nodes("#REVIEWS .innerBubble")

date <- reviews %>%
  html_node(".rating .ratingDate") %>%
  html_attr("title")
> date
 [1] "December 9, 2014" "December 9, 2014" "December 8, 2014" "December 8, 2014"
 [5] "December 6, 2014" "December 5, 2014" "December 5, 2014" "December 3, 2014"
 [9] "December 3, 2014" "December 3, 2014"

Based on this output, I would use the following format: %B %e, %Y (or %B%e, %Y depending on what "with a leading space for a single-digit number" actually means WRT to the leading space; see ?strptime).

Yet, both fails:

strptime(date, "%B %e, %Y")
strptime(date, "%B%e, %Y")

I suppose it's due to the fact that %B expects the month names to be in German instead of English:

Full month name in the current locale. (Also matches abbreviated name on input.)

---

EDIT

Sys.setlocale() let's you change your locale settings. But it seems that it's not possible to do so after a function relying on locale settings has been called. I.e., you need to start with a fresh R session in order for the locale change to take effect. This makes temporary changes a bit cumbersome. Any ideas how to work around this?

This is my locale:

> Sys.getlocale(category = "LC_ALL")
[1] "LC_COLLATE=German_Germany.1252;LC_CTYPE=German_Germany.1252;LC_MONETARY=German_Germany.1252;LC_NUMERIC=C;LC_TIME=German_Germany.1252"

When I change it before running strptime() for the first time, everything works just fine:

Sys.setlocale(category = "LC_ALL", locale = "us")
> strptime(date, "%B %e, %Y")
 [1] "2014-12-09 CET" "2014-12-09 CET" "2014-12-08 CET" "2014-12-08 CET" "2014-12-06 CET"
 [6] "2014-12-05 CET" "2014-12-05 CET" "2014-12-03 CET" "2014-12-03 CET" "2014-12-03 CET"

However, if I change it after having run stptime(), the change does not seem to be recognized

> Sys.setlocale(category = "LC_ALL", locale = "German")
[1] "LC_COLLATE=German_Germany.1252;LC_CTYPE=German_Germany.1252;LC_MONETARY=German_Germany.1252;LC_NUMERIC=C;LC_TIME=German_Germany.1252"
> strptime(date, "%B %e, %Y")
 [1] "2014-12-09 CET" "2014-12-09 CET" "2014-12-08 CET" "2014-12-08 CET" "2014-12-06 CET"
 [6] "2014-12-05 CET" "2014-12-05 CET" "2014-12-03 CET" "2014-12-03 CET" "2014-12-03 CET"

This should actually result in a vector of NAs if the change back to a German locale had been carried out.

Answer 1

parse_date_time() from the lubridate package is what you are looking for. It has an explicit locale option for parsing strings according to a specific locale.

parse_date_time(date, orders = "B d, Y", locale = "us")

gives you:

[1] "2016-02-26 UTC" "2016-02-26 UTC" "2016-02-26 UTC" "2016-02-24 UTC" "2016-02-23 UTC" "2016-02-21 UTC"
[7] "2016-02-21 UTC" "2016-02-21 UTC" "2016-02-20 UTC" "2016-02-20 UTC"

Note that you give the parsing format without leading %as you would in strptime().

Answer 2

You can also use readr::locale("en") inside readr::parse_date()

  readr::parse_date(date, format = "%B %e, %Y", 
              # vector of strings to be interpreted as missing values:
                na = c("", "NA"), 
                locale = readr::locale("en"), 
              # to trim leading and trailing whitespaces:
                trim_ws = TRUE)

From the docs: "The locale controls defaults that vary from place to place. The default locale is US-centric (like R), but you can use locale() to create your own locale that controls things like the default time zone, encoding, decimal mark, big mark, and day/month names."