The documentation of 'base::cut' says: ... the factor level labels are constructed as "(b1, b2]", "(b2, b3]" etc... In reality, the spaces after the commas are missing. I like the documented behavior better than the actual, though. > sessionInfo() R version 3.5.1 (2018-07-02) Platform: x86_64-pc-linux-gnu (64-bit) Running under: Ubuntu 18.04.1 LTS gb