I would like to propose a .Internal() POSIXct2Date() function, similar to do_POSIXlt2D() in src/main/datetime.c. I created a working prototype, which is now included in Dirk Eddelbuettel's RApiDatetime package: https://github.com/eddelbuettel/rapidatetime This prototype is a combination of asPOSIXlt and POSIXlt2D from R Core. The functions are essentially concatenated, with the extraneous parts removed. Directly converting from POSIXct to Date uses less memory and is roughly twice as fast. You can find the relevant bits in the commit on GitHub: https://github.com/eddelbuettel/rapidatetime/commit/6bc9320451fb1e62d53b5012d33acf538c0f50c6#diff-7df5c1a674e930a4d93ba45f3ce0aaaf Would someone on R Core be interested in adding this function? If so, I can create a patch that includes all the necessary code additions needed to make it a .Internal() function. Thanks for your consideration! Best, Josh -- Joshua Ulrich | about.me/joshuaulrich FOSS Trading | www.fosstrading.com R/Finance 2018 | www.rinfinance.com