I make a new post in order to specifically solve this issue. I tried my best but can't fix this.
When I tried to download LMERConvenienceFunctions packages, I get at some point:
checking for X... no
configure: error: X11 not found but required, configure aborted.
ERROR: configuration failed for package ‘rgl’
1: In install.packages("LMERConvenienceFunctions") :
installation of package ‘rgl’ had non-zero exit status
2: In install.packages("LMERConvenienceFunctions") :
installation of package ‘LMERConvenienceFunctions’ had non-zero exit status
I am on LINUX, Unbuntu LTS Bionic Beaver.
Thank you very much for the help ~