Is there a string formatting operator in R similar to Python's %?

Question

I have a url that I need to send a request to using date variables. The https address takes the date variables. I'd like to assign the dates to the address string using something like the formatting operator % in Python. Does R have a similar operator or do I need to rely on paste()?

# Example variables
year = "2008"
mnth = "1"
day = "31"

This is what I would do in Python 2.7:

url = "https:.../KBOS/%s/%s/%s/DailyHistory.html" % (year, mnth, day)

Or using .format() in 3.+.

The only I'd know to do in R seems verbose and relies on paste:

url_start = "https:.../KBOS/"
url_end = "/DailyHistory.html"
paste(url_start, year, "/", mnth, "/", day, url_end)

Is there a better way of doing this?

Maybe something like `paste(url_start, paste(year,mnth,day,sep="/"), url_end)` — CPak, Sep 06 '17 at 22:38
See https://stackoverflow.com/questions/17475803/sprintf-format-strings-reference-by-name/17476306#17476306 — G. Grothendieck, Sep 06 '17 at 23:45

LyzandeR · Accepted Answer · 2017-09-06T22:58:42.417

74

The equivalent in R is sprintf:

year = "2008"
mnth = "1"
day = "31"
url = sprintf("https:.../KBOS/%s/%s/%s/DailyHistory.html", year, mnth, day)
#[1] "https:.../KBOS/2008/1/31/DailyHistory.html"

Also, although I think it is an overkill, you could define an operator yourself too.

`%--%` <- function(x, y) {

  do.call(sprintf, c(list(x), y))

}

"https:.../KBOS/%s/%s/%s/DailyHistory.html" %--% c(year, mnth, day)
#[1] "https:.../KBOS/2008/1/31/DailyHistory.html"

edited Sep 06 '17 at 22:58

answered Sep 06 '17 at 22:41

LyzandeR

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3

Maybe also worth showing an example illustrating vectorization like `"https:.../KBOS/%s/%s/%s/DailyHistory.html" %--% list(1999:2000, mnth, day)` or the sprintf equivalent. (I guess in python they would loop this sort of thing instead.) – Frank Sep 07 '17 at 00:06
Gets tricky when you've got other percentage characters in your text...for example an SQL query with wildcard operators. – John F Aug 05 '20 at 16:17

austensen · Answer 2 · 2018-03-28T12:56:31.480

44

As an alternative to sprintf, you might want to check out glue.

Update: In stringr 1.2.0 they've added a wrapper function of glue::glue(), str_glue()

library(glue)

year = "2008"
mnth = "1"
day = "31"
url = glue("https:.../KBOS/{year}/{mnth}/{day}/DailyHistory.html")

url

#> https:.../KBOS/2008/1/31/DailyHistory.html

edited Mar 28 '18 at 12:56

answered Sep 06 '17 at 22:53

austensen

2,857
13
24

score 11 · Answer 3 · answered Sep 07 '17 at 05:16

The stringr package has the str_interp() function:

year = "2008"
mnth = "1"
day = "31"
stringr::str_interp("https:.../KBOS/${year}/${mnth}/${day}/DailyHistory.html")

[1] "https:.../KBOS/2008/1/31/DailyHistory.html"

or using a list (note that now numeric values are passed):

stringr::str_interp("https:.../KBOS/${year}/${mnth}/${day}/DailyHistory.html", 
                            list(year = 2008, mnth = 1, day = 31))

[1] "https:.../KBOS/2008/1/31/DailyHistory.html"

BTW, formatting directives can also be passed, e.g., if the month fields needs to be two characters wide:

stringr::str_interp("https:.../KBOS/${year}/$[02i]{mnth}/${day}/DailyHistory.html", 
                    list(year = 2008, mnth = 1, day = 31))

[1] "https:.../KBOS/2008/01/31/DailyHistory.html"

this is the closest to the flexible `format` in python. looks quite nice. — MichaelChirico, Mar 28 '18 at 09:11

Is there a string formatting operator in R similar to Python's %?

3 Answers3

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