R Tip: Use seq_len() to Avoid The Backwards Sequence Bug

February 19, 2018
By

(This article was first published on R – Win-Vector Blog, and kindly contributed to R-bloggers)

Another R tip. Use seq_len() to avoid The backwards seqeunce bug.

Many R users use the “colon sequence” notation to build sequences. For example:

for(i in 1:5) {
  print(paste(i, i*i))
}
#> [1] "1 1"
#> [1] "2 4"
#> [1] "3 9"
#> [1] "4 16"

However, the colon notation can be unsafe as it does not properly handle the empty sequence case:

n <- 0

1:n
#> [1] 1 0

Notice the above example built a reversed sequence, instead of an empty sequence. To avoid this use seq_len():

seq_len(5)
#> [1] 1 2 3 4 5

n <- 0
seq_len(n)
#> integer(0)

integer(0)” is a length zero sequence of integers (not a sequence containing the value zero).

To leave a comment for the author, please follow the link and comment on their blog: R – Win-Vector Blog.

R-bloggers.com offers daily e-mail updates about R news and tutorials on topics such as: Data science, Big Data, R jobs, visualization (ggplot2, Boxplots, maps, animation), programming (RStudio, Sweave, LaTeX, SQL, Eclipse, git, hadoop, Web Scraping) statistics (regression, PCA, time series, trading) and more...



If you got this far, why not subscribe for updates from the site? Choose your flavor: e-mail, twitter, RSS, or facebook...

Comments are closed.

Search R-bloggers

Sponsors

Never miss an update!
Subscribe to R-bloggers to receive
e-mails with the latest R posts.
(You will not see this message again.)

Click here to close (This popup will not appear again)