Shuchi Mishra thinks this is interesting: Like the double bracket notation, this returns the list component in its native data type (in this case, a numeric vector of length one). From 2. Managing and Understanding Data from Machine Learning with R - Second Edition by Brett Lantz Publisher: Packt Publishing Released: July 2015 Note V. Imp Share this highlight http://www.safaribooksonline.com/a/machine-learning-with/10127737/ Twitter Facebook Google Plus Email Get Instant Access Now Start a Free Trial Learn about Safari for Business Have an account? Sign in. Minimise Unlock the rest of Machine Learning with R - Second Edition and 30,000 other books and videos By clicking this box, you confirm that you have read and agree to the terms and conditions of our Membership Agreement, and you understand that when your trial period ends, you will be required to provide billing information if you wish to continue using the service. Unlock the rest of this book Start a Free 10-Day Trial loading Learn about Safari for Business Have an account? Sign in.