Using sprintf with multiple variables of different length in R

Question

I am working with R trying to use the sprintf function to print multiple urls. The URL is in the form http://www.weather.unh.edu/data/year/day.txt. I want to print the url for each day of multiple years. I tried:

day <-c(1:365) year <-c(2001:2004) urls<- sprintf("http://www.weather.unh.edu/data/%s/%s.txt", year, day)

but received the error

Error in sprintf("http://www.weather.unh.edu/data/%s/%s.txt", year, day) : arguments cannot be recycled to the same length

I am printing these urls so I can import raw data from them in bulk. If anyone has any idea how to make this work with sprintf or another function please let me know

user295691 · Accepted Answer · 2015-08-12 20:32:57Z

1

What you want is expand.grid to generate the combinations of years and days.

times <- expand.grid(days=1:365, years=2001:2004)
urls <- sprintf("http://www.weather.unh.edu/data/%s/%s.txt", times$year, times$days)
head(urls)
[1] "http://www.weather.unh.edu/data/2001/1.txt"
[2] "http://www.weather.unh.edu/data/2001/2.txt"
[3] "http://www.weather.unh.edu/data/2001/3.txt"
[4] "http://www.weather.unh.edu/data/2001/4.txt"
[5] "http://www.weather.unh.edu/data/2001/5.txt"
[6] "http://www.weather.unh.edu/data/2001/6.txt"

That said, this will encounter problems with leap years, etc; you might want to consider seq.Date instead, like

dates <- as.POSIXlt(seq.Date(as.Date("2010-01-01"), as.Date("2014-12-31"), by="day"))

And then

urls <- sprintf(".../%s/%s", dates$year + 1900, dates$yday)

edited Aug 12, 2015 at 20:32

answered Aug 12, 2015 at 20:25

user295691

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Comments

robbrit · Accepted Answer · 2014-07-24 15:54:03Z

0

You can use a for loop:

days <- c(1:365)
years <- c(2001:2004)
urls <- c()

for (year in years) {
  for (day in days) {
    urls <- c(urls, sprintf("http://www.weather.unh.edu/data/%s/%s.txt", year, day))
  }
}

answered Jul 24, 2014 at 15:54

robbrit

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MagicScout · Accepted Answer · 2014-07-24 16:06:07Z

0

your running into a wall because it can't recycle the values you gave it. (365/4 is not a whole number).

Just make one string out of the two and then use sprintf

day  <- c(1:365)
year <- c(2001:2004)
day.year <- paste(rep(year,each = 365),day,sep = '/')
sprintf('http://www.weather.unh.edu/data/%s.txt',day.year)

Cheers.

answered Jul 24, 2014 at 16:06

MagicScout

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