# Avoiding unnecessary memory allocations in R

[This article was first published on

Want to share your content on R-bloggers? click here if you have a blog, or here if you don't.

As a rule, everything I discover in R has already been discussed by Hadley Wickham. In this case, he writes:**bioCS**, and kindly contributed to R-bloggers]. (You can report issue about the content on this page here)Want to share your content on R-bloggers? click here if you have a blog, or here if you don't.

The reason why the C++ function is faster is subtle, and relates to memory management. The R version needs to create an intermediate vector the same length as y (x – ys), and allocating memory is an expensive operation. The C++ function avoids this overhead because it uses an intermediate scalar.In my case, I want to count the number of items in a vector below a certain threshold. R will allocate a new vector for the result of the comparison, and then sum over that vector. It’s possible to speed that up about ten-fold by directly counting in C++:

Often this won’t be the bottleneck, but may be useful at some point.

To

**leave a comment**for the author, please follow the link and comment on their blog:**bioCS**.R-bloggers.com offers

**daily e-mail updates**about R news and tutorials about learning R and many other topics. Click here if you're looking to post or find an R/data-science job.

Want to share your content on R-bloggers? click here if you have a blog, or here if you don't.